Check which SSID your Sonos are using and get the phone to use the same one.
Also check that something like a VPN isn't altering the expected address.
Also, make sure your phone is connected to the same device as your Sonos is. If you have two different (but similarly or the same named) SSIDs, you’ll have two networks (subnets) and the phone may be connecting to one, and the speakers to the other. That’s if you still have both the xFinity router and the eero setup. In general, if one is getting a signal from the other, it needs to be set up in bridge mode, so both aren’t generating a WiFi signal.
Thank you.
I’ve put the eero in bridge mode and will see how it goes.
Very grateful for the help.