List your state of art headphones for smart phone use!

I agree with mijostyn re: the Etymotic Research ER-4. They are very small, light, portable, relatively inexpensive, durable, noise-isolating, and (most importantly from the audiophile perspective) they sound quite good. I use them with an Audioquest JitterBug and the DragonFly Red when I'm on extended airplane flights (fortunately, not that often) and when I'm sitting outside reading or staring into space. Better yet, they actually stay in place and sound good when exercising (e.g., a half or full marathon). Only problem: microphonics (noise from the cords) unless you're stationary.
Keith

Not sure if state of the art but have given me literally 100,s of thousands of miles of service.
In fact when I watch my fellow travelers all unpacking their  bulky over ear phones and looking for charging ports I can’t help but chuckle.
I drag out my pocket this tiny black pouch with my own phones inside and plug and play.

Klipsch R6, still using my original from 6 years ago and I am a Delta Million Miler and I hammer the heck out of them.
I did buy a pair of the R6 mk2 but not even opened them yet.
All phones I have used them with have more than enough grunt to satisfy me, makes watching an in-flight movie more tolerable too.
Ultimate bass maybe a bit shy but mids and treble are superb.
Oh and 6 hour flight comfortable guaranteed!

On ear but:

https://www.amazon.com/gp/product/B008AT6DMC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Uber, my Shure E4 - the same.

The main reason I started looking for better was just that being so old, I got curious, especially at the multi-driver IEM’s out there, and of course, wanted the convenience of bluetooth.

I would have stuck with Shure but the buyer reviews were mixed for the reliability, so tried the FH5 with press that made them sound like state of the art, and finally the Hifiman pair.

I’m keeping the Shures as my back up pair, the Hifiman go in my daily work bag and everything else is going into a box I’d like to be buried with so no one else knows of my mistakes.

My new favorites are JH Audio Roxanne custom fit IEM. They are molded to your ear so they seal perfectly and are extremely comfortable. Dynamics, Treble, Bass are all excellent. I replaced Audeze LCD-3 and Foster THK900Mk2 and haven’t looked back.