New iPhone - now upsized - set for release in September

App developers need to be poised for a redesign because Apple's iPhone is getting bigger.

The tech giant will roll out the iPhone 6 in two sizes - 4.7 inch and 5.5 inch - in September, according to industry insiders who have seen the prototypes.

The new iPhone screen will be made entirely from scratch-resistant sapphire crystal glass, they said. Sapphire crystal, second to diamond as the hardest material, is now used by Apple for its iPhone camera lens cover and touch identification.

It will also sport a new display at 441 pixels per inch (ppi), the same as the Samsung Galaxy S4. The highest definition Apple now offers has only 326 ppi.

"They have to tackle the phablet [devices that serve as both phone and tablet] market. People want bigger screens now," one insider said.

The iPhone 5S, Apple's largest phone at 4 inches, is notably smaller than the S4, which measures 5 inches, and the Galaxy Note 3, with a 5.7 inch screen.