Have all the Contacts disappeared on your iPhone?
Each of your contacts are stored in one or more Groups and it is quite easy to hide them accidentally
This can result in your contact looking like this...
Here's how show your Contacts
1. Open Contacts (tap the Contacts icon) - looks like this...
2. Tap Groups (top left)
3. Tap Show All Contacts (top left)
4. Tap Done (top right)