Q: I just switch my phone number. How to change Authentication Phone Number for office 365?
A: There are two different situations.
1. The old phone or phone number still work.
Please refer to this post:
How to change MFA verification method
2. The old phone or phone number doesn’t work.
Please refer to this post:
One way or other, you need to have the follow screen popup for you to change the phone number.
Or view this step by step video:
