It's not one way, it's two way on at least one of the channels. This has been explained a few times on the board here. My understanding re the video data is there's a check involved, so once the controller receives video data, the controller will send info back to the Phantom confirming receipt and asking if the data sent is good and not corrupted. If the phantom answers yes it's correct and not corrupted, the data is then sent from the controller to the mobile device.
This is why if you're going to add an amp, you want one that works both ways. You want one that amplifies the outgoing signal, and one that also amplifies the incoming signal.
This is one of the advantages of Lightbridge - there is no check.