Complex sentence: In September 2014, Apple released the iPhone 6 Plus along with its 2014 iPhone models; the first iOS phablet, with the largest iPhone screen to date, at 5.5 inches.
Split into simpler sentences: In September 2014, Apple released the iPhone 6 Plus as part of its iPhone models for 2014. The device is the first iOS phablet, and has the largest screen of any iPhone model to date, at 5.5 inches.