If your iPhone screen is not responding to touch. The first thing to try is force-restarting your phone, as this will probably fix any system glitch causing the phone's touch behavior to be sluggish or unresponsive. Make sure the screen is clean and dry as well because dust or wet areas can also affect how sensitive to touches the screen reacts. Also, it might be useful to see if you have any protective screen accessories on that you could take away, like a screen matte or a phone case, if their placement was causing a problem. Also, keep an eye on iOS updates, as you need to be sure that the problem is not with you and not the system itself. Should nothing of what was mentioned before help, then the most likely cause for the malfunctions is internal hardware damage, and in such cases, it is best to go to a service center where a professional can identify the type of problem and offer you a solution.