FaceTime icon missing on iPhone 5. How do I get it back?

Help! FaceTime icon has vanished on my iPhone 5...beginning to wonder if it was ever there!

How do I get it back? It is part of the Apple built-in Apps. I can ask Siri to use FaceTime and it is on the buttons in contacts and both links work... but the icon is not on my home screen anywhere! I have it on my iPad.. so shouldn't it be on my iPhone as well?