What phone do you have that the jellyfin app and the jellyamp app are unavailable?

Edit: Also you can support subsonic with jellysub acting as a go-between. Considering its not a music-first solution, I'm not surprised that it doesn't support subsonic natively, personally.

Edit 2: Its unmaintained but works as of the last time I tried it out, fwiw. It isnt exactly a complex codebase either if something got tripped up by minor changes.