To change a user’s authentication phone number in Microsoft 365, an administrator needs to access the user’s authentication methods in the Microsoft 365 admin center or Azure Active Directory (Azure AD). The administrator can then update the phone number associated with the user’s multi-factor authentication (MFA) settings.
Steps to Change User Authentication Phone Number (Admin):
• Access the Microsoft 365 Admin Center: Log in as an administrator to the Microsoft 365 admin center (admin.microsoft.com).
• Navigate to all admin centers then select Microsoft Entra
Navigate to all users the search the user name
Click the user name then click authentication methods
You can edite the phone number for authentication by clicking the three dots there
