Phone repair experts are saying they're seeing more and more iPhone 6 and iPhone 6 Plus devices with the same issue: a non-responsive display and a grey line running at the top of their screens.
iFixit says that some phone repair outfits are getting around a hundred of the defective phones and the cause isn't the screen themselves, but the chips controlling said displays. The chips involved are the two touchscreen controller or Touch IC chips, which are on the board. Thus replacing the screen does not fix the phone.
One phone repair person even likened the issue to a "ticking bomb" just waiting to show up in iPhone 6 and iPhone 6 Plus phones. Most ordinary phone repair outfits aren't qualified to do changes to the boards directly but there are repair experts who can perform microsoldering and perform direct repairs on the board. It is a cheaper option than replacing the whole board or buying a new phone.
Why is this problem so endemic with these models? It might, experts posit, have something to do with 'Bendgate' or the design flaws that made the iPhone 6 and 6 Plus bendier than they should have been.
If you're wondering why the iPhone 6s and 6s Plus aren't affected, it's because the affected chips have been moved to the display assembly, leaving them less vulnerable to any flex in the phone.
So if you're starting to see issues with your iPhone 6-range device and it's under warranty, send it to get fixed ASAP. Apple however has not commented on the Touch IC controller issue. Safe to say if you're not planning on getting the latest iPhone, you might be better off going for nothing less than an iPhone 6s, and resist the urge to buy an older iPhone 6 or 6 Plus.