I can't feel my iphone 5s vibrate when it's on silent, and I receive a call or text?

It does work but I can't feel it in pocket, I have an apple leather case, so what should I do?

First off when it's on silent it's supposed to vibrate

Figure out just how much money you lose when you are delayed returning a call. It was just a few years ago that, if you were out and about, you didn't return a call until you got home.

On settings make sure you enabled vibrate on silent