After recent iOS upgrades (it seems), my Sonos 1 speaker stopped showing up as a choice from my iPhone. I have done no other changes, to my network or the router setup. I did try deleting my Sonos app and reinstalling it.
The odd part is that I can still play to my Sonos from my iMac by choosing on the AirPlay drop down.
I can also play to my Sonos speaker from the iPhone Sonos app - see below, but no longer as a drop down anymore from the iPhone home screen. In the attached, I am playing music to my Sonos, through the app. but the second attachment, the speaker is not showing, even though the music is actually playing to the speaker from my phone
I used to be able to select my Sonos speaker (Name of speaker = “Home”) from the drop down here.