1. Click the profile icon in the upper right corner of the screen on the Teams Phone.
2. Click Settings from the Device Menu.
3. Scroll down and click Sign out from the Settings Menu.
4. Click OK to confirm sign out.
Additional Info
Instructions to Sign in to a Yealink Teams Phone on a computer or on the phone itself can be found here: Sign in to Teams Phone on a Computer, Sign in to a Teams Phone on the Phone