Use Airplay instead.

No good if you’ve no Wi-Fi 

How are you even using Apple Music without wifi?

4g

Hi @Nottsjed 

Welcome to the Sonos Community!

First, please try rebooting your iPhone.

Also, when you get audio interruptions, it could be due to your internet connection over 4G - does the same happen when you just play from the iPhone speaker?

Finally, try playing music stored physically on your iPhone - if that works without issue, and you determined the issue isn’t due to your connection, then the problem may be that you are asking more of the iPhone’s radio than it can deliver (receiving the stream while simultaneously broadcasting it twice).

If none of this helps, I can’t recommend much other than contacting Apple Support.