Calls Go to Voicemail

I have in iPhone 13 Pro Max. The phone will intermittently start going straight to voicemail. Airplane mode - Off, Focus Off, Do Not Disturb - Off, Not Silenced. No Carrier Update needed. Using correct iOS. I have reset to factory settings twice. Then I checked my iWatch. On my iWatch I turned mirror my phone” off and on, and now my phone rings.

This has also happened on my iPhone 12 which is connected to another iWatch. I had to do do the same thing.

This is NOT an issue with the carrier, it is a flaw in the iOS. I hope someone from Apple sees this and can get it fixed. Like I said this has been happening intermittently on both phones for a year.