iOS 11.3 (build 15E5178f) is an official Apple over-the-air update for the iPhone 6, released on 2018-02-06T18:21:26Z. The update package is 305.13 MB. This is a delta (partial) update that requires 11.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9c60c85e18878f6702699c5b2f389fcfab38d454.zip.