iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone 6, released on 2018-03-29T17:12:30Z. The update package is 685.1 MB. This is a delta (partial) update that requires 11.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9af08863fc5f358e7a0af09b0d13674bca8877e9.zip.