Hi
If there is a hardware issue and you had the screen replaced by Apple or an Apple Authorised Service Provider, then the issue may be covered under the repair warranty. Repair terms may vary by country. In the US and UK, for example, Apple warrants screen repairs for 90 days against defects in materials and workmanship - or for the remaining term of your Apple Limited Warranty (or AppleCare+ coverage, if you have it), whichever is longer.
If the screen was replaced elsewhere, you may wish to check whether that service provider warranties their repair work and, if so, to return the iPhone to them for further service.
Your iPhone may otherwise be eligible for chargeable repair service. Contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your iPhone to be inspected and, if service is recommended and your iPhone is eligible, to establish your available service options, timescales and the cost: