The way Microsoft has made Windows Phone is that it backs up your contacts to the Microsoft Account automatically. You can simply login to Outlook.com, and get access to your contacts there, and can even export them. The problem with this is that not many people are aware this option exists, and secondly it only leaves you at the mercy of Microsoft. So if for some reason you loose access to your MS account, you’re without a backup.
I frequently get asked if there is a way to manually backup contacts on Windows Phone, and this post answers that question. While there is no inbuilt mechanism that you can use, there is a free app that gets the job done. Download Contacts Backup from the Windows Phone store.