iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 6, released on 2018-04-24T17:10:34Z. The update package is 32.34 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: c14dc9a6a64f160d39dd3e1e43926efb35d9cfa3.zip.