My recommendation is to connect in this order:
Turn controller on
Turn Phantom on and allow for a connection.
Plug the display device into the controller
Once into the app you should see a "Ready to Fly" message
When you ay that you show something is disconnected, what is it that is not connecting? I'm guessing the app? If this is the case, clear the app cache, delete the app and reinstall.
Correction: I read your post again and it seems that you cannot connect the controller to the Phantom. If this is the case, it has nothing to do with the display device.