Like most consumer communication apps, Microsoft Teams (free) relies on your mobile number to find and connect to your friends and family. Adding a mobile number to your Microsoft account will help you find others and for others to find you in Teams. Learn more about managing how people find you and what contact information others can view in Microsoft Teams (free).
Adding a mobile number as a sign-in alias enables you to sign in conveniently using your phone number instead of your email. It also adds an extra layer of security to your Microsoft account. However, there can only be one mobile number as a sign-in alias because when you sign in with a mobile number, we need to know which account it's for.
Learn more about how to add a phone number to your Microsoft account.
For more help, contact support or ask a question in the Microsoft Teams Community.