Hmm, have you tried to check these troubleshooting steps here: https://yt.be/help/hsQV ? If that doesn't do the trick, send more details/screenshots of the issue. Keep us posted!
Basing from the screenshot you sent, I can see that the button to add a new phone number is available. If the phone number that you added is already associated to an account, this error will show as 2 account can be verified per phone number in a year.