Missed Calls Without Automatically Dialing Them Back

Review View and delete the call history on your iPhone for some advice, which states "You can also delete specific calls by swiping left on the call and tapping Delete."

Make sure you start the swiping motion before touching the contact. If you are not satisfied with that method, make sure that you provide iPhone Feedback.

I rarely delete Missed Calls but when I do, I start swiping from right to left very near the right edge of the phone. It also works if I start the swipe from right to left just a bit above the phone number and lower my finger to the phone while my finger is moving right to left. Both ways avoid tapping the phone number which will dial it.