According to Chinese site C Technology [Google Translate, via Unwired View], Apple has begun testing a next-generation iPhone prototype with a 4.9-inch display, along with an iPhone 5c successor sporting a larger screen. The claim is somewhat different from one made by Bloomberg earlier this month stating that Apple was developing two next-generation iPhones that would feature curved displays at 4.7 and 5.5 inches, although it is likely that the company is testing various screen sizes as it often does during a development cycle.
Currently, Apple's iPhone 5s and iPhone 5c both feature 4-inch Retina displays, compared to competitors like Samsung's Galaxy S4 that feature 5-inch displays. MacRumors released a printable papercraft version of a 5-inch iPhone back in February of this year after other rumors of a larger iPhone surfaced.
Article Link: Larger-Screen iPhone Rumors Continue with 4.9-Inch iPhone 6, iPhone 5c Successor