Phone won't take incoming VOIP calls?

Check your iPhone settings

Go to Settings and turn on Airplane Mode, wait five seconds, then turn it off. Check Do Not Disturb. Go to Settings > Focus > Do Not Disturb and make sure it's turned off. Check for any blocked phone numbers.

If you can't make or receive calls on your iPhone - Apple Support

There seems to be a solution in this by ATT --> https://forums.att.com/conversations/apple/not-receiving-voip-phone-calls-on-my-iphone/6112805b2ace6a75f0bbfa93

Badabeng wrote:

I think it must be in the Apple ID since it follows it from phone to phone and from Verizon to ATT.

There is nothing in the Apple ID which will block VoIP calls unless these numbers are blocked by you.

These blocked numbers will remain with you for every device that uses this Apple ID.

This may help you --> HELP! Can make outgoing VoIP calls but no incoming