If you have contacts synced to your device from many sources (iCloud, Gmail, Outlook, Yahoo, Facebook, etc.) you may have one person with multiple contacts in your phone. Link these contacts together for a better experience.
From one of the duplicate contacts tap on Edit in the top right corner and scroll to the bottom of the screen. Here you'll find the Linked Contacts section - now tap on "link contacts..." and select the duplicate contact. Repeat this process for as many times as you have duplicates. Tap Done in the top right when complete.
This tip works for iPhone, iPad, iPod Touch, and on all recent versions of iOS.