How can i improve the sound of Iphone 11?

I am using SE846 earphones into Ibasso DX90 and i love the sound. I recently bought TIDAL for streaming at home. 
I tried listened to TIDAL through my iphone 11 into SE846 and obviously, with no DAC in it, it was not as good as when using DX90. 

There are times i cannot carry the DX90 but will have my phone with me.

Is there a dongle i can put between the Iphone and SE846 that will improve the sound to match that of my DX90?
Have you thought about iPhone 11 > Apple Lightning to USB > AQ Dragonfly? 
Dragonfly will be able to decode MQA. I personally utilized this combo when walking - dongle and Dragonfly add a bit to the phone, but not too distracting if you bend the dongle and the Dragonfly lays behind the iPhone (in your pocket for example). 
I found a step-down trafo (2:1) improved the SQ of my Meizu phone. A bit bulky to carry around though.
"Have you thought about iPhone 11 > Apple Lightning to USB > AQ Dragonfly?"

This is a good possibility. Getting a  (Apple Lightning to USB) is easy enough, and the Dragonfly isnt big, but i never heard it and wonder if it will sound as good as the DX90.

Or if another mini dac would do better. A quick google search for "best portable dacs" revealed different reviewer opionions. No one agrees which is best - Cobalt, Audiolab M-DAC nano,  Clarus CODA USB DACm,  THX Onyx,  Maktar Spectra X2, etc.
Had a Dragonfly black. Sounded fine, especially when out in the noisy world. Sold it after I got the Questyle QP2r and never did an a/b comparison. Considering getting a cobalt for my desktop, which can serve double duty…
I used a cypher labs 720 dac with my iPhone and it sounded very good. I also used it between my Mac and desktop speakers
I prefer my Chord Hugo 2 but when I'm traveling light I love my AudioQuest Dragonfly Cobalt.  It delivers amazing sound in such a convenient small size.  I bought an AudioQuest Dragonfly Red when I misplaced my Cobalt and was surprised that an even more affordable DAC can sound so good.  The Cobalt has a lower noise floor, generally sounds better and is smaller in size, but the Red is really all you will need if you will be mainly using it in environments where you may hear some of the background sound.  After listening to both of them side-by-side I can easily hear that the Cobalt is clearer, more precise, has tighter deeper bass and more natural extended highs, a greater sense of depth and width to the soundstage, and an overall more pleasing sound than the Red. It really is worth the extra $100.
I use an Apple Lightening to USB adapter from my iPhone to a Dragonfly Red to drive my Hifiman planar ‘phones and it improves the sound significantly over using the iPhone itself.  Specifically the soundstage expands and clarity and detail are greatly improved as well.  In short, it brings back all the audiophile goodies that make music more enjoyable.  I don’t think you’d be disappointed by the sound, and it’s easy to use on the go.  The Lightening to USB3 adapter is supposed to sound better and gives you the capability to charge your phone while listening, which is nice to have.  And the Cobalt might sound even better although I haven’t felt the itch to upgrade from the Red.  

One thing I’d recommend is trying Qobuz — I switched from Tidal and am much happier, and no MQA crap to deal with.  Anyway, hope this helps, and best of luck. 
Im also using the SE846 direct to my iphone. The sound sounded “dead” without the Audioquest Dragonfly Cobalt. Sounds perfect with it. I also use the Lavricables pure silver lightning to usb A adaptor. It gives that effortless air in the sound. 
I have a Dragonfly Black with the Jitterbug and it improves the sound of all phones I've tried it with. The Red or Cobalt are probably even better. I also have an iFi Nano but it sounds about the same, it is just much bigger and hard to carry.
I have a PS Audio Dectet conditioner and I've been happy with it so far. It also helps with power surges. 
I know you have an Apple but what I did for my Android was install UAPP app. There is also an app within that app for a "Bit Perfect" app. Then you use an OTG USB cable. 

The UAPP makes the Android's DAC better. Perhaps there is a similar app for an Apple phone? 
I have a Helm Audio Bolt DAC that I have been pretty happy with. It's a USB C dongle DAC that I use with a Samsung S21. With an android phone I'm using USB Audio Player Pro to stream Tidal and Qobuz and I have no complaints. 
I intend to go this route for my iPhone 11 PM. iPhone--lightning to USB C--THX AAA Onyx. The Onyx decodes MQA.

I'll be using this low cost, Lightning to female USB C adapter. 

My only worry is the known issue where the iPhone's Lightning port supplies little to no power to attached devices. 
Portable DAC is big improvement. Personality I use AQ Dragonfly Cobalt and very happy with it. Also if you using Apple Music hi res service you can improve SQ with the phone Settings. Go to Phone Settings then to Music where in Audio section you could play with Audio Quality, EQ, Dolby Atmos etc.

Happy listening.
I struggled with this question for a long time. Traveling with amps and a DACs. It was heavy and bulky or a mass of interconnections.

My solution was to switch to highly efficient headphones designed to be driven by low power. I bought a pair of Ultrasonde Edition 8 that sound great driven directly from the iPhone.

The best solution depend on the circumstances you use the system. In particular, the ambient noise you will be experiencing. I enjoyed this solution for many years. But I realized I was fine leaving “high end” sound at home and traveling in comfort (+200,000 miles a year) was more important and switched to Bose QuietComfort. Not highly accurate but really enjoyable (like your favorite inexpensive wine as opposed to a $250 bottle of Bordeaux) to listen to and incredibly comfortable and could be worn with noice cancelation only in airports and airplanes. 

So, depends on your usage.
I've been using the Hidizs S9 dongle with an iPhone and I get great results.   There are both single-ended and balanced outputs, and a lot of power.   It sounds great and it also measures quite well.
Thank you for all the replies. I am seeing a lot of love for the Dragonfly solution. The Hidizs and Helm are much less expensive. I am thinking i would be able to get much of the purchase price back on a Dragonfly if i did not like and sold it on the used market.

 - What is a jitterbug? Only one user mentioned having it.

" One thing I’d recommend is trying Qobuz — I switched from Tidal and am much happier, and no MQA crap to deal with."

When using the BluOS app, Tidal tracks list either CD or MQA.
When using the TIDAL app, tracks show M (master) or nothing.

Is MQA something to be avoided due to reduced sound quality? I have been unable to hear a diff between any of the formats (when the same song is listed twice - CD and MQA. I am paying for the TIDAL HIFI level which should not limit my choices.

Is MQA something to be avoided due to reduced sound quality?
Currently I’m subscribed to Qobuz, Tidal and Apple Music I have to admit that SQ of Tidal Masters is very close to SQ of Qobuz Studio Premier (album varies) some albums better on Tidal some on Qobuz…both services have their pluses and minuses. For me as a practical listener the MQA is definitely not a thing to avoid a specially on mobile setup. Don’t hesitate to try it yourself. It’s not big deal to get trial subscription for both services for one month so you could figure out yourself. I don’t yet have proper equipment to check Apple Music on my main system but using Dragonfly Cobalt DAC with Senheiser HD650 let me conclude that Apples Hi-Res Masters SQ is better than both Tidal Masters and Qobuz SQ (same album)…so the issue is yes practical for the listener… we r just choosing the better option and at some choices MQA is exist.
"and no MQA crap to deal with."
Nothing to deal with.
Dragonfly handles MQA seamlessly and with great results.