An iPhone is my favourite controller. It’s used with Airplay and native apps like BBC Sounds, Spotify and TIDAL to my headless Allo DigiOne player, which is hard-wired to the network and running Volumio or Moode most of the time.
I do have CD playback and bit-perfect FLAC ripping set up too, which can all be controlled via phone browser, but to be honest, I rarely bother unless it’s not available on Spotify or TIDAL.