Yep, it's definitely a phone sized device, and you can see her scrolling with her finger in the reflection, so it's a touch screen. Now, what's actually unique about it that separates it from the millions of similar devices, I guess we'll have to wait and see. Perhaps the display stays square to your head? I mean, if you're viewing the screen at a slight angle, it skews the perspective to look straight?
There's a quick photoshop of a phone at an angle and the display square. Now, you wouldn't purposely use the phone at such an extreme angle, but when you're typing, playing games, in bed, etc, it might make things easier to use. Fairly straightforward, it would just be tracking the location of your head, and adjust the perspective of the display.
We still can't rule out a phone, though. For this type of video they don't necessarily use the real device. Another possibility (as suggested by the questions in the form) is that it's a sensor applicable to many types of devices.
Tough to see much, but you do see a shadow of her hand and the proportions indicate to me a tablet-sized device not a phone.