Because of misconfigured or inaccurate display settings and options, your iPhone touchscreen may not perform as intended at times. In reality, many iPhone owners who have had sluggish touchscreen issues have found relief by tweaking their device's 3D touch settings. It wouldn't hurt if you gave it a shot and saw how it turned out. Here are some options:

1. To access the Settings menu, tap Settings.
2. From the settings, scroll down to General and hit it.
3. To continue, tap Accessibility.
4. To see and access more choices, tap 3D Touch.
5. Adjust or alter the sensitivity settings as necessary.
6. Restart your iPhone after making modifications to the 3D Touch settings.