I accidentally deleted my "contacts" app on my iPhone. How do I get it back?
Unless you have jailbroken your phone you can't delete the Contacts app. Most probably it's either in a folder or on a screen somewhere. To find it again


press the Home button repeatedly until the search screen is shown
Type "Contacts"
Select Contacts app from search results


If you can't find it, you could always back up your phone (to save the current settings) and also take screen shots of the various screens you have set up. Then go to the settings app and Reset the home screen layout.

Worst case is you wait while you restore your backup if this doesn't return contacts to the first screen.