I have had Sonos working using my old iPhone for 3 years.
I recently upgraded the handset and have had nothing but issues with the Sonos connection.
I have rebooted the router and reset the Sonos App many times.
Sometimes it will eventually find my speakers only to drop them again the following day.
I still have my old phone and it connects ok.
IT is really getting on my nerves now - it seems nothing but issues!