Hello @Carol Lai MS Graph provides authentication method APIs to manage a user's authentication methods. Using these APIs you can add a phone number for a user, who can then use that number for SMS and voice call authentication if they're enabled to use it by policy. Please see documentation to add new phone numbers for the user and authentication methods API overview. Note that phoneAuthenticationMethod is currently in beta.
Please let me know whether this helps and if you have further questions,
Diana.