Update iPhones over the air with private server I've a more than 20 iPhone 5s/6/6s in my company. I normally download IPSW and update using iTunes so that the updates do not take all the internet bandwidth.

I would like to know if it's possible create our own server and publish those updates such that users can update their phone by Wi-Fi. That way instead of downloading updates directly from Apple it will download from my private server.
You can run the Caching service, part of server.app. The Caching service supports OTA updates for iOS 7 and later. All you need to do is enable the service in Server.app. Devices do not need to be part of MDM supervision.


  macOS and iOS devices automatically access the available caching service on the network they’re currently connected to


You can find Apple's documentation of the Caching service at:


https://help.apple.com/serverapp/mac/#/apd74DDE89F-08D2-4E0A-A5CD-155E345EFB83