Unable to determine if your iPhone display is a genuine Apple part. This could be because the part is non-genuine, not functioning as expected, or the installation is incomplete.

I think the message says it all. If you had the screen replaced by a third party, this will let future potential owners of the iPhone that a non-genuine part has been installed. If you had not had the screen replaced, then it may be failing and you will need to take it to the Apple Store or Authorized Apple repair center. As with any error you get, you should always restart your phone first as a basic troubleshooting step to verify if the error remains.