This is a user-to-user technical support site. We are not Apple.
The current released iOS version is 11.2.6
iOS 11.3 is in beta testing. It is possible to signup for the beta software, assuming you are willing to have things go terribly wrong with your iPhone. In my opinion, you should ONLY put beta software on a sparse device, not your day-to-day device.
You can send Apple iPhone Feedback at
<https://www.apple.com/feedback/iphone.html>
They will not reply, but it does get read.