airplay mirror? then no, as has been pointed unless it's a 5 in landscape it won't match the aspect ratio.
since you're saying box in the middle, i'm guessing this is what you're doing.
and just to cover all the bases, you have rotated your phone?
regular airplay depends on each app's developers as to weither it is supported or not. For example if you're watching something in the stock video player, it will take over the full screen, all you will see is the video, so no bar at the top or playback controls on the TV. (and as long as it's 16:9, so most recent television shows for example, it will take up the full screen.)
videos that you watch in safari will do this also.