Ok, so you’re not using AirPlay 2 at all, you’re using the Sonos controller. Although I don’t know which OS is running on your iPhone.
Have you tried removing the Apple connection from the Sonos controller completely, waiting five minutes, then setting it up again?
For some reason, undetermined at this moment, your speakers are having difficulty reaching the Apple authorization servers. There are all sorts of possibilities there, none of them are clear yet, based on what information has been provided. I tend to dismiss DNS issues, due to the fact that the Apple Music app works on your phone.
It could be simple wifi interference causing your speakers to not be able to reach those auth servers, or something more.
Have you submitted a system diagnostic within 10 minutes of experiencing this problem, and called Sonos Support to discuss it?
There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.
When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.
One thing I’d try in the meantime is to run the Apple Music app on your iPhone, and then pull down from the upper right corner of the screen. This gives you access to the AirPlay 2 screen, and you can then select those Sonos speakers that are responding to an AirPlay 2 request. Likely not your surround speakers, but your Beam and your Port should be reporting there. That would completely skip using the Sonos system, and use AirPlay 2 from your iPhone and send the audio directly to the speakers.