Managing personal Outlook.com account settings, security, and privacy
Hello, thank you for reaching out to Microsoft Q&A.
The phone number you see in the Microsoft account profile section is used to sign in to your Microsoft account. The landline number you see is for security information, which is used to verify that you are the account owner. That is,
you can use your mobile phone number as your sign-in credential (instead of your email address). However, for verification, you previously added your landline number, which cannot receive SMS codes.
In this situation, you will have to replace the security information -
On the verify your identity screen, select "i don't have any of these" and follow the prompts to replace the security information.
Note - If you remove all of your previous security information and replace it with something new, your account will be put into a restricted state for 30 days.