For clarification, PlayFab doesn't support registering or logging in player accounts based on the phone authentication. To integrate phone numbers to the authentication information of player accounts, you can let players set phone numbers as usernames, so they can use them and fixed passwords to register and log in accounts. Please note, in this case, your players still need to add the contact emails to their accounts so that they can be authenticated when they forget the passwords. You can also check this thread - Login/Signup with phone number - Playfab Community for more information.
If you need the official support for the phone authentication of player accounts, you can try to add a feature request for it.
As PlayFab supports OpenID Connect, you can find a OpenID Connect provider that supports login/signup with phone number and then integrate it with PlayFab. For example, you can use Azure AD B2C as the provider.
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