Do you mean when you are using your Spotify app but casting to one of your Sonos speakers? Not sure what else you can mean by ‘playing music on wifi mode’.

I’ve just started a track in the Spotify app, then tapped the speaker icon, selected one of my Sonos speakers, and the music plays on there. When I use the physical volume up and down buttons on the phone, the volume of the speaker goes up and down. It works when I have the phone locked too. 

It’s an iPhone 14. 

Is this what you mean?

Ok, example. I’m using Sonos Move. You can play music by connecting it with Bluetooth or „streaming” through Wifi.

The issue is with the second option. So, i open Spotify, then tap available devices list, then tap on that Sonos Move (which is connected to my WiFi). When i’m connected to a speaker and start playing music, i press physical volume buttons, and a small window pops up (look at the screeenshot in the topic). If i want to change the volume, i have to click „—" or „+”, or adjust it with „green line”. It’s the only way. The physical buttons are not working. When i try to use them, it changes the volume of Iphone speaker. I had the same problem few months ago, then it dissapeared, and now it’s back out of nowhere. 

Don’t confuse this problem with AirPlay mode.

It’s not the problem with my iPhone buttons, beacuse they work normally on blueetooth mode with Sonos, and also with Airpods etc. etc.

I’m using Iphone 14 pro, both iOS and Sonos software are updated, Spotify app as well.

 I actually prefer that behavior.  I can see though how it might be convenient to use the phone to adjust volume.  My issue with the phone controlling the volume is when I use AirPlay.  I need to have the phone on nearly full volume to get an acceptable volume level and if I forgot to lower the volume before quitting AirPlay I will likely blow up the speakers.  Not sure if it would behave like this now.  Don’t need AirPlay anyway.