Connect your iPhone to your Windows computer. Plug the wider end of the syncing cable into the base of your iPhone and plug the USB end into the USB port of your computer. Open iTunes if it does not automatically open when you connect your iPhone.
Go to the "Devices" tab in the left sidebar of iTunes and select your iPhone.
Select the "Info" tab on the main screen in iTunes.
In the "Contacts" section on the "Info" page, check "Sync Microsoft Outlook Contacts". Choose whether to sync all of your contacts or only specific groups of contacts.
Navigate down the page to the "Advanced" section. Make sure that "Contacts" is not selected. This will protect the contacts on your iPhone from being replaced and deleted.
Click the "Apply" button at the bottom right corner of iTunes. Your iPhone and Windows computer will sync all your contact information.