iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone 6, released on 2018-03-29T17:12:28Z. The update package is 1.34 GB. This is a delta (partial) update that requires 10.3.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: cc8d33c895782998bc2d2634f07fe5111e17c44f.zip.