Try deleting and re-installing the Sonos app and rebooting your phone.

Also read this article:

https://support.sonos.com/s/article/3690?language=en_US

Thanks for the reply. I did as you suggested and unfortunately it did not solve the issue. 

Not sure what’s going on.

I’m able to use my volume buttons on iOS 15.0.1, on an iPhone 13, running Sonos S2 version 13.3. This is while the Sonos app is in the front/live. Are you trying to do this with the phone locked?

Nope. When I’m in the actual Sonos app. I just checked my wife’s iPhone (iPhone 12 on OS 14.6) and the volume doesn’t change on hers either. Both phones are running the latest Sonos app update. 

Odd. Completely working on my phone, as I just tested it. 

Perhaps it’s time to submit a diagnostic, and contact Sonos directly?

I have a similar problem. 
I play my music always directly from Apple Music  and i airplay? To sonos?  In Apple Music I can’t use the volume slider anymore. If I move it, it jumps to any other strange position and sonos volume is dropping to any direction. It seems the sync between both is completely on the loose. I don’t have this issue when “airplaying” to other devices. 

I do have exactly the same problem. Since iOS15.0.1 and 15.1 I can not use slider in Apple Music while connected to Sonos via Airplay. Jumping around and muting my Sonos a thousand times while sliding.

Any solution for this?

Same exact problem here. Re-installing the app does not fix the issue.

The Sonos device volume control, using hardware buttons, is working on my iPhone XR too, I’m running iOS 15.1 - Sonos S2 App v13.3.2

iPadOS 15.1 buttons are also working. 

Same problem here on 13PM , it does this :

https://streamable.com/d6wbfa

I can change the volume only if I use the physical button first.

2 others videos of what happens 

Controlled by the Sonos App :

https://streamable.com/3di8ws

Controlled by Airplay

https://streamable.com/yeb2id

Isn’t that a different thing to the thread topic, which is about being unable to control the volume at all using the hardware buttons on the phone - but appreciate you may have an issue with Airplay, but what is the actual Airplay volume slider showing on your phone and which actual iOS App are you using as your Airplay source?

If I use Apple Music to Airplay to a Sonos speaker then the volume slider control in both AM/Airplay display and the Sonos App seem to be okay on the iPhone XR running iOS 15.1

Have the same issue. Controlling volume via the slider in Apple Music is not working properly. Just slides to zero if I‘m trying to adjust it. Using the buttons is working perfectly.

This issue is not present while using Spotify via Airplay.

This happened after upgrading to iOS 15.x.

I’m on iOS 15.1 and loving the change to the volume control slider on the Sonos App.  A number is now associated with the volume setting and with my iPhone 8 a haptic response is also felt when adjusting the volume slider.  Pretty cool!  
 

I also think the sound quality from my Sonos Amp has gotten better when listening to Spotify.  It’s similar to what I’ve gotten when improving my turntable.  I’m going through old favorite songs and they are sounding more musical.