Add mobile number

The missing Add phone number option is expected for some personal Microsoft accounts because Microsoft is phasing out SMS for authentication and account recovery; use a recovery email, Microsoft Authenticator, or a passkey instead.^1^

Add another verification method

1. Open the Microsoft account Security page:
   https://account.microsoft.com/security
2. Sign in with your personal Outlook.com/Microsoft account.
3. Select Manage how I sign in.
4. Select Add a new way to sign in or verify.
5. Choose one of the options displayed:
   • Email address — add an email address you can access and enter the verification code sent there.
   • Microsoft Authenticator — use the app to approve sign-ins.
   • Passkey — sign in using your device’s face recognition, fingerprint, or PIN.
6. Complete the on-screen verification. The new method should then appear among your sign-in options.^2^

If Phone number does not appear in that menu, it cannot currently be added as a new security method to that account. This is not an Outlook browser or device setting. A verified recovery email and passkey are Microsoft’s supported replacements for SMS.^1^

References

1. Microsoft to stop sending SMS codes for personal accounts
2. Microsoft account security info & verification codes | Microsoft Support