Good question.
If you have hard wired your Naim to your router… then the Naim should working as a Streamer, DAC, and integrated amp. So the phone should not be involved… other than a controller. So, the Naim can select between inputs… Bluetooth, wifi… etc. you want the input ?Ethernet?… or whatever the name is. Or try wifi. Avoid any roaring through Bluetooth or apple AirPlay. These are inferior protocols.
If you are communication correctly.. then let’s look at the file resolution.
Did I interpret you question / situation correctly?