Who can change your phone number depends on the permissions on your account.
If you are an employee
You cannot change your own phone number in Teamso. Your number is shown on your profile page but cannot be edited there. You need to ask your company's HR manager.
If you have permission to update employees
You can update the number with the edit (pencil) icon on that employee's record. This icon only appears for accounts that have the employee update permission.
Your phone number is used both for signing in and for one-time approval codes, so it is worth checking that sign-in and approvals still work after the number changes.