Okay, I googgled it (typo pun intended). My VR goggles give me 74 degree FOV with a 5.5" phone. Thats basically the same as the headplay (72) and way better than any fatshark. To give you an idea what that means, Id say that field of view is comparable to wearing a scuba goggle.
Resolution will be about the same too with a 1080p phone. The headplay does 1280x800 with a single screen, your phone will probably give you 1080P or better, divided per 2 (one for each eye), in both cases you get about what the phantom sends anyway, so better doesnt help. Well maybe it does in theory, due to the VR deforming you might lose some quality if your phone doesnt have a higher resolution than your FPV source material, but then you're splitting hairs. And you might well have a UHD capable phone.