sharing music from my iPhone library

When you play your library on your phone what app are you using?  You can use AirPlay if the app you use to play music is not integrated in the Sonos app.

Technically, it’s AirPlay 2 ;)

I often use that, or Bluetooth, with the speakers that can accept it, but then I have to use a ‘player’ based on my iPhone, and not the Sonos controller, since Apple has blocked that. 

Apple does not allow the Sonos app access to the music that is stored on your phone. So AirPlay (2) is the way to go.