New iPhone: How to re-pair with Family Watches

I recently replaced an iPhone 13 Pro with a new iPhone 14 Pro. My son's Apple Watch SE (1st Generation) was paired with my old phone using Family Setup. The new iPhone shows "Pairing Not Complete" under the Family Watches for his watch. If I tap "Finish Pairing" I get the following pop up message...

From what I can tell, the only solution is to unpair his watch using the "Forget this Apple Watch" option and re-pair it. A couple questions...

1. Is there a way to do this without also resetting the watch?
2. If not possible, will it have continued backing up to iCloud (as watches setup using Family setup should) despite being unpaired from my iPhone such that we can restore from backup? Is this even an option with Family Setup?
3. Will restoring from a backup allow him to keep the same phone number or will I need to create a new plan?

Thanks.