Hi Aisha
I am Dave, an Independent Advisor, I will help you with this . . .
If you want to change the phone No. on your Microsoft Account:
Log into this page:
https://go.microsoft.com/fwlink/?LinkId=529489
Select Add a phone number
Select your country from the list
Enter the phone number you want to use, and then select Next
When you add a new phone number, Microsoft will send a text message to that number to verify it
Enter the code in the text message, and then select Next