Something error with my lcd

i bought 2nd iphone 6 plus. Few days ago just when i try to buy hardcase, I put iphone from the top first into the hardcase. Then suddenly the Screen was “blink-blink” on the top screen only and i can not touch the screen. But the machine it was normal, i could use home button and power button. Then after 10minute the phone back to normal.

But now sometimes the top of the screen was like “blink2” again and touchscreen totaly off when the screen show the blink. It was like someone push the screen on the top until nothing i can do unless wait it came normal again. But when it happened again, i try to press the phone on front camera area, and that make the phone back to normal.

Sorry for my english

Could u suggest me what i supposed to do?