The iTunes sync process normally syncs contacts found in your iPhone’s Contacts application to your computer’s address book application. Using a special setting in iTunes, you can use the sync process to replace the information in your iPhone’s Contacts application with the information from your computer’s address book application. This feature also allows potentially allows you to delete your iPhone’s contacts using the iTunes sync process.
Connect your iPhone to your computer using the data cable.
Double-click the iTunes icon on your computer.
Select your iPhone from the list of “Devices” within iTunes.
Click the “Info” tab. Select the “Sync Address Book Contacts” option.
Click the “Sync” button. Your iPhone will sync with your computer and transfer all of the contacts from your iPhone to your computer’s address book application.
Double-click the icon for the address book application on your computer.
Delete all contacts that you want to remove from your iPhone. To delete a contact, select the individual contact and press the “Delete” button on your computer’s keyboard.
Select the “Sync Address Book Contacts” option in iTunes.
Scroll down and select the “Contacts” option under the “Advanced” subsection.
Click the “Apply” button to sync your iPhone with the address book application on your computer. During this second sync, iTunes will remove all of the contacts you deleted on your computer’s address book application from your iPhone’s Contacts application.