According to new information from the China Times translated by BrightWire, Apple is planning to release the iPhone 5S alongside a larger phone, deemed the "iPhone Math" by the report From MacRumors:

Because the iPhone Math name is highly unusual and does not fit in with Apple's traditional naming scheme, it is not clear if it is a code name or a potential mistranslation. China Times says that the larger phone will come equipped with a 4.8-inch screen and an 8-megapixel camera. It is said that it will launch in June alongside an updated iPhone 5, which will also feature an 8-megapixel camera. An additional iPhone update is said to be coming during the holiday season, with a 12-megapixel camera.

 Apple Rumored to Debut 4.8-Inch 'iPhone Math' in June