Touch disease is an Apple defect most common on the iPhone 6 Plus. It happens when the touch IC chip comes loose on the logic board. This leads to the phone freezing and not being able to touch anything on the screen even though you can see the screen. Most of the time the screen just freezes and then unfreezes on its own. However eventually over time it will get worse to the point of not being able to do anything for hours or even at all.
Apple can fix the issue for $149 however, they may take about 2 weeks or more to get it fixed unless you go to the Apple store. The closest one in our area is in Tulsa Oklahoma. Another option would be to go on eBay and search “Touch Disease Repair.” Look through the listings and reviews and you should be able to find a company that can do it under $60. Again it takes about 2 weeks for you to send it to them and get it back but it is a much more affordable way to go. Most of the time they will have a 30-90 day warranty; however the repair does not always prevent it from coming back.
To be honest in our opinion the best route is to get a newer phone. The only phones that we know of that have had these issues is the iPhone 6 and 6 Plus. Apple fixed the issue on the 6S, 6S Plus, and newer.