Anyone who already has a current license to OW1 should not have to add a phone number.
Phone numbers should be applied to only brand new accounts with no OW1 license.
If a phone number cannot be added, have a requirement to make a purchase no less than $10 to have an active OW2 account. Pretty much the cost of one Battle Pass.
Offer something for free if you link a phone number, like how it’s done in WoW.
My number works perfectly fine for OW2. These are merely sensical suggestions to help resolve a phone number issue whilst also mitigating any potential cheating issues.
EDIT: I have a number that works but great news today: