If you've got a cracked screen and faulty touch issues, or recently dropped the phone, your first step should be to check with a replacement screen installation. Use an iFixit Guide to learn how to install the screen, and see if a replacement fixes the problem.
Even if your screen isn't cracked, the issue could still be related to a damaged screen that just needs to be replaced.
Similarly, if a replacement screen solves the problem it may resurface down the line after a few hours or days. This is less likely a defective screen and more likely an issue with "Touch Disease" affecting your phone.