You cannot change the keyboard sensitivity. Whats going on with your phone? Does it not pick up your finger taps? Do you have to click it twice? Is it too sensitive?
If this is your first iPhone? I can tell you from my experience when I first got a iPhone several years ago. I had trouble typing . Now its become second nature after using it and I never had any trouble. Except when I have many apps open. Thats usually when I click on a key and it takes a second to respond. All I do is close the apps running in the background and it becomes normal again.