Built in ear speaker doesn’t work after replacing screen

Did you transfer the earpiece/cable from the old display or did your new replacement come with all those parts pre-installed? I’ve had some issues (very occasionally) with full display assemblies that come with the small parts, and usually switching out that proximity cable or the entire display (for another full assembly) fixes it. Otherwise it’s possible you stressed the cable during removal or reinstallation and you’ll need to put in a new front-camera/earpiece/proximity cable.