If your school has a zero cell phone policy, you can prevent students from signing in with their mobile phones by following this guide.
From the admin view, click Rooms.
Click "Options" at the top right of the Rooms page.
Toggle off "Allow students to use phones" to disable students from signing in with their mobile devices.
When a student tries to sign in on a mobile device, this is what will show on their screen:
This feature disables students from signing in using an iPhone, iPod Touch, and Android phones (both app and web browser). Logging in using iPads, laptops, or computers is still allowed.
NOTE: Digital IDs still work on disabled mobile devices.