iPhone 6 is when they got bigger and better. Before iPhone 6, they were in small and compact pocket sizes, unlike the other smartphones. It was released in September 2014 in three colors, Silver, Gold and Space grey. It has 4.7 inches screen with Retina Display.
iPhone 6 was built with 1GB RAM and released in three variants of storage spaces of 16GB, 32GB, and 64GB. It has a 1.4 GHz dual-core processor with an A8 chipset. The rear camera is of 8MP enabled with autofocus and face detection. The front camera was set to 1.2 MP. But the iPhone 6 is now only compatible with iOS 8 version.
It was released at a price of around $400 back then but can get for very much less price. But you might have to find this at any authorized seller as Apple stopped selling from its direct stores.