Do you mean the phone number linked to your Microsoft account?
You could try the following steps to change your phone number:
- Log in to your Microsoft account at account.microsoft.com.
- Click Security.
- Under Security basics, click on UPDATE INFO button under Update your security info.
- Verify the last 4 digits of your phone number and it will send you the verification code at that number.
- Enter the verification code correctly and you will be redirect to the Security settings page.
- Beside of the phone number displayed on your computer, there is a Remove button. Click on it to remove your number.
- Once the phone number is remove, click on Add security info add the new number and click Next.
- Enter the code that was sent to your new number.
- Once the code is entered correctly, it will display the new information.
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