To add a phone number as a sign-in alias for a personal Microsoft account:
- Open Edit account info: https://account.live.com/names/manage
- Sign in.
- Select Add phone number.
- Follow the prompts to verify the number and add it to the account.
If the page only shows Add email and not Add phone number, use the account info page directly and try again from there. A Microsoft Q&A recommendation also suggests trying:
- a private/incognito browser window
- a different browser
- clearing cache and cookies
- a different device or network
Also check that the phone number is not already associated with another Microsoft account.
Important distinction:
- Account info / alias = phone number used to sign in
- Security info = methods used to receive verification codes
For security info, Microsoft states that for increased security, a new phone number can no longer be added as a new way to verify sign-in. On the Security tab, available options include email, an authenticator app, or a passkey.