@dasan is right. Something caused this to happen. Phones don't break all by themselves. It technically can happen, but this would not be the result. If the display connectors aren't placed properly I could see this happening, also this looks like damage to the display. I would recommend reseating the connections using this guide
iPhone 6 Front Panel Assembly Replacement
If that doesn't take, I would recommend using this display, you could save some loot, buying it somewheres else, but you'll likely yield bad results. Part doesn't work, then how to exchange? You can't
iPhone 6 LCD Screen and Digitizer Full Assembly
@dasan. This is not personal. I'm trying to reward you. Learn English better, yes you're right we should be learning your language better. But, I'm sorry, that will never happen. Why I can't say. Thank you for helping. You sound like a good repair technician. Keep helping here! Please! We would love to have you helping in the community! Together we are strong! I know you have information we don't. This site is for sharing information and fixing answers, so we can help! It is a thankless job, which I'm working on that part
Man, I'm just tryin to have a scotch and check my order status...