It looks to be more about the aspect ratio of the device display as opposed to whether its a tablet/mobile. I say this as I was able to run a little test with a Galaxy S4:It seems that the 3,992 x 2,992 resolution (12MP) is only available if you are shooting from a tablet (just confirmed with an iPad). The file when the Inspire 1 is controlled from an iPhone (6 Plus) is cropped (By the 'smarts' in the camera - not user selectable) to 3,992 x 2,242 (9MP), so by using a tablet to fly the Inspire you can get 33% more pixels than from an iPhone.
With its default 1920x1080 display resolution JPG photos are taken at 4000x2250 (DNG=3992x2242).
Using an app to switch resolution 1440x1080 (4:3 aspect ratio) JPG photos now start coming out at 4000x3000 (DNG=3992x2992)!
How very bonkers!