How can get this message to go away because my phone is fine

You had the phone serviced by an unauthorized shop. They do not have legitimate access to genuine Apple parts and they do not have any access to the tools necessary to properly install them.

If it works for you, great. Apple more than likely won't touch it if it ever needs service again. They may agree to replace the display that's currently installed with a genuine screen, and do it the right way, but you'll have to pay, and if the servicer managed to damage anything internally during the install, they will refuse.

As it stands, it is unsupportable and has no trade in value were you to decide you wanted to trade it for an upgrade.

You don’t. It is not “fine”. It has a non-Apple display installed or a display that was installed by an unauthorized party without access to the tools required to do so properly.

If the display has NOT been replaced, the something has failed and the phone needs to be serviced by Apple or an authorized service provider.

It’s not supposed to go away.

It’s permanent.

Did you have the display replaced by someone?

It means that you have a part installed on the phone that is not an Apple part and/or was not installed by an authorized service provider. Your phone may still work just fine. However, you may have forfeited the ability to get future service from Apple.

It's also there so that if the phone is ever sold or given to another person, they have accurate knowledge of what repairs have been done to the phone.

The message cannot be controlled by you.

As the article above and Kilted Tim suggest, you had an unauthorized service performed on your iPhone. This is the result.