Editing contacts creates a duplicate
Does the duplicate appear on your iPhone or within your iCloud account. 

Try editing your iPhone contacts directly via this tool for example:

http://www.copytrans.net/iphone-contacts.php

Also, where do you edit the contact entries from which the duplicates result - on your iPhone or within the iCloud. I would assume that if you are editing them on the iPhone, a temporary local copy is created on your iPhone until it is synced back to the iCloud after which the duplicate copy (physically residing on your iPhone) will be gone.