How do I delete all contacts on the iphone (iOs 8.3), but NOT a full phone erasure?

How do I delete all contacts on the iphone (iOs 8.3), but NOT a full phone erasure? I want to keep the loaded music and all apps, etc, (to give phone to my child), so only want to erase contacts -- can only find how to do it one-by-one contact? Easy to erase texts, messages and emails without resetting the entire phone, but cannot find how to bulk erase all contacts.