Phantom scroll and tap has pretty well been identified as a flex issue...
http://forums.windowscentral.com/nokia-lumia-1520/297759-6.htm
If you lay your phone screen down on a table is it flat? Or do opposite corners rise up?
If you have flex induced twist to the phone you need to adjust your carry habits. Due to the large size, if you habitually carry it in pants pockets it can get torqued and the polycarbonite body retains the shape of the phone curving to fit against your thigh. I no longer carry my phone in any but the roomiest trouser pockets. Breast pockets are now preferred or I also have a carry pouch and a belt holster.
You can carefully, gently and patiently bend the phone back to true (or nearly so) and it corrects many of these issues as things realign inside the phone.