Add alternative/additional security method (SMS/Call)
Go to https://mysignins.microsoft.com/security-info and click “Add method”.  

Alternative method 1

Select the method you would like to add. e.g. Phone 

Alternative method 2

Enter your country code and mobile number. Select “Text me a code” or “Call Me”

Alternative method 3

You will receive a verification code via SMS/Call

Enter the code and click Next.

Alternative method 4