This was a function in the past, Apple stopped that so unfortunately it’s not something that will return.
 

The Sonoe app does not actually play music but instructs the player to play from a chosen source which is why Music playing apps on the iPhone can play the music but apps like Sonos and Bluesound cannot.

What you can do, with newer Sonos devices, is use AirPlay 2 to send a signal from iOS. Something I do fairly frequently. I think the Sonos One was the first device that could accept an AirPlay 2 signal, older devices were designed long before AirPlay 2 was a twinkle in Apple’s eyes. 
 

For me, once I get the signal to my Sonos One, I can then group that speaker, using the Sonos controller app, with any other Sonos ‘room’. That way, I can use my PLAY:1s as a grouped speakers, and hear my AirPlay 2 signal through them. 

oh yeah - now I remember … totally forgot how it unfolded lol. Thanks.

Thanks I have one speaker with airplay and I do what you suggesteed, but it doesn’t work perfectly, and can be annoying when I try to hook in my other 6 speakers + sub.

Huh. There must be something odd going on, I don’t have any issue. You may want to submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.