add a phone number

Add the phone number as a sign-in alias through Your info → Manage how you sign in to Microsoft → Add phone number, rather than through the basic profile fields.

Add the number

1. Sign in at https://account.microsoft.com/profile.
2. Select Your info.
3. Select Manage how you sign in to Microsoft.
4. Select Add phone number.
5. Enter the number and complete the verification prompts. Microsoft documents this route for adding a phone-number alias.^1^

If Add or Next is still missing

This can be a page-rendering or browser-session problem. Try these in order:

1. Open an InPrivate/incognito window, sign in again, and return to the profile page.
2. If the control remains missing, try a different browser or device.
3. Clear the browser’s cookies and cache for Microsoft account sites, then sign in again.
4. Try another network, such as a mobile hotspot.^2^

Also, a phone number can be associated with only one Microsoft account. If Microsoft reports that the number is already linked, select Change number and use another number; recently reassigned mobile numbers can still be associated with a previous owner’s account.^3^

If the number is for verification codes instead

A sign-in alias and a security verification method are different. For security verification:

1. Open the Microsoft account Security tab.
2. Select Manage how I sign in.
3. Select Add a new way to sign in or verify.

The phone-number option may not be available for security verification. If it is absent, use a recovery email, Microsoft Authenticator, or a passkey instead.^4^

If Add phone number remains absent specifically under Manage how you sign in to Microsoft after the browser tests, use Microsoft’s Contact Support option. Support can troubleshoot the page, although agents cannot directly change account details.^5^

References

1. "Something went wrong" with error ADDriverStoreAccessNonLocalException | Microsoft Support
2. How do I add my phone number to my sign in details? - Microsoft Q&A
3. Help with reusing phone numbers in a Microsoft account | Microsoft Support
4. Microsoft account security info & verification codes | Microsoft Support
5. Change the email address for your Microsoft account | Microsoft Support