Rumors continue to swirl about a bigger screen on the next iPhone. 9to5Mac:
Apple will not just increase the size of the display and leave the current resolution, but will actually be adding pixels to the display. The new iPhone display resolution will be 640 x 1136. That’s an extra 176 pixels longer of a display. The screen will be the same 1.9632 inches wide, but will grow to 3.484 inches tall. This new resolution is very close to a 16:9 screen ratio, so this means that 16:9 videos can play full screen at their native aspect ratio.
It's clear that Apple is at least testing prototypes of a larger-screen iPhone. Whether they'll actually be released is another question. At this point, I wouldn't be surprised to see a new iPhone with a bigger screen, but I also wouldn't be surprised to see the screen stay the same.