If you've had an iPhone 8 screen replacement not by Apple or Phone Bar, you must not install iOS 11.3 as your screen could stop working.
Apple haven't officially acknowledged the problem yet but small independent repair shops are reporting that many iPhone 8 screens they've replaced have stopped working after the latest iOS version is installed.
Screens replaced by Phone Bar do not have this problem as we only use 100% genuine screens.
The same thing happened with the release of iOS 11 with iPhone 6s screens that weren't genuine - again, something Phone Bar did not have a problem with as we only use original Apple screens in our replacements.
Right now, the only way to fix this is to have a genuine screen replacement by a reputable company - hopefully in the future Apple will release an update which will fix the issue although it's not currently known when this will be.
You can book a repair online with Phone Bar here.