It took me a moment to figure out that with an appropriate case (ie. one that let me snap or strap a phone to the back and connect with USB), this would appear

It took me a moment to figure out that with an appropriate case (ie. one that let me snap or strap a phone to the back and connect with USB), this would appear to work as an entirely functional e-reader, rather than only as a satellite display and input device. Alternatively, you could possibly tether it with Bluetooth LTE, and skip the case, keeping the phone in your pocket. Whether connected via USB or BT, it would make it an 'upgradable' ereader in a sense, by swapping out the phone it is tethered to.