Enabling Teams for a user and assigning telephone number using Graph API is not possible.
However, you can follow below documents which explains how to manage teams and user access using PowerShell script along with assigning telephone number to user.
Managing Teams and user access:
1.https://learn.microsoft.com/en-us/microsoftteams/teams-powershell-managing-teams
2.https://learn.microsoft.com/en-us/microsoftteams/user-access
Assigning phone number to a user or a resource account:
1.https://learn.microsoft.com/en-us/powershell/module/teams/set-csphonenumberassignment?view=teams-ps
2.https://learn.microsoft.com/en-us/microsoftteams/assign-change-or-remove-a-phone-number-for-a-user
Thanks,
Prasad Das
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