Here are a few things you should check if your video is not displaying properly in a Teams call on your mobile device:

1. Ensure that your mobile device is up-to-date and running on the latest version of your operating system.
2. Restart your device.
3. Check that network connection options are enabled.
4. Check the power-saving settings on your mobile device.
5. Check if there are any unresolved issues related to your video device.
6. Try connecting to the Teams call from a different mobile device.