Overflow:hidden does not work on mobile safari for some reason, and the frame stretches because of that. Is there another way to prevent the frame from showing the overflown content? visit this website http://tinyurl.com/a9n3mog on an IOS device to see what i mean.
I see the bottom of the phone sticking out of the div and the bottom border is gone. Is that what you mean? In any event, I use overflow hidden all the time on responsive sites and this is never an issue but many things affect each other. There is plenty of suspect code in your source. As a test case, I would make a simple jsfiddle or code pen with just an image in a box that it smaller then itself and see what happens.