Try deleting and reinstalling the Sonos app and reboot your phone.

If the App reset, re-install, reboot is not successful, reboot the SONOS products. Refrain from any SONOS Factory Reset without further consult.

Also, check the microphone on the iOS device in use, to ensure it’s not obstructed. Remove any case for that device, too. If memory serves, the microphone in use is not the large one that you’d speak in, but the pinhole one that often is next to the camera lens. There have been a few report in these forum of those being covered by dirt. 

I never realized there was a second mike, on my list of things to keep an eye on now. Thanks

It’s pretty small, and fairly easy to get ‘blocked’ by crud. I’m only 75% sure that this is the microphone they use, but worth keeping clean, as Apple uses this to measure ambient noise to deal with telephone usage. 

Actually, during the process you have to turn the iPhone around with the main (bottom) mike facing up, so Sonos has taken that into account. It is not using the secondary mike on the iPhone. But thanks for the input. 

Yes. I did have a chat with a support person at Sonos. They said to switch off Trueplay and re-enable it and then run it. I will try that today. No rebooting or factory reset anything. But I wish retuning would be simpler.

Now that I think about it, I actually think both are in use, but I’ll be interested in your experience. 

This worked for me. Thanks for sharing.