Accessing Microsoft Teams Free using personal or organizational credentials
As an alternate option, Microsoft advises using the Microsoft authenticator app to receive a verification code.
To look further, there is the possibility that you get this error because your phone number is associated with an existing Microsoft account as an alias. If so, you'll not be able to use it unless you remove it from that account.
To unlink your phone number, please go to
https://account.live.com/names/manage and login with your phone number in question.
After login in, you can remove the phone number from the account and reuse it.
For more, see https://support.microsoft.com/en-us/account-bil...
Please let me know the outcome, and I'll look further into this.
Regards
Nik