White lines appear on my iPhone 5 touch screen when I dropped it with an otterbox?

Hello, I went to the movie theatre with my iPhone 5 that I purchased from Verizon about 6 months ago and dropped it on the tile floor in the lobby. My phone had the otterbox defender on it and one half a centimeter thich line appeared on the screen when I picked it up and unlocked. I can't unlock my phone because the touch screen does not work on the white line. This makes type incredibly difficult and I would like to know if there is anything I can do to fix it or if my phone is under warranty? How do I check if I have warranty from Apple?