Why is there a white line at the bottom of my iPhone screen?

My iPhone 5 has been working perfectly normal until earlier when for no reason a thin white line appears at the bottom of my screen. It will continuously reappears every few seconds then goes off. When it does appear, my iPhone become unresponsive to any touch meaning it is taking so long to type even a few words like the screen freezes or to even swipe across. I'm really unsure why it has happened as it was perfectly fine before and I haven't dropped it or anything today.

Does anyone know what this means? Will I have to replace anything?

That is what the NSA makes the screen do when monitoring your phone.