The phone stops making calls
Every other day or so, my 12 pro max stops being able to make calls. "call failed". It works again after I restart the phone but its a hassle.
iPhone 12 Pro Max
Try first to optimize the range of the mobile network, see this Apple article:
If you see No Service or Searching on your iPhone or iPad
If you see No Service or Searching on your iPhone or iPad - Apple Support
Then see this Apple article: If you can't make or receive calls on your iPhone
If you can't make or receive calls on your iPhone - Apple Support