How to Unify Contacts on Your iPhone
When you import or access contacts from different sources on your iPhone, the result could be multiple information records for one contact. Unify a contact by linking multiple records that have the same name. A unified contact doesn't merge the information but does display all the information for one person on one record.
If the names aren't exactly the same, two records appear but you can manually link contacts and designate the top unified contact by doing the following:
Tap a contact that has more than one record, and then tap Edit.
Tap the Link Contact field at the bottom of the Info screen.
Your list of contacts opens.
Tap the name of the contact you want to link to the first contact.
Tap the Link button in the upper right corner.
To unlink contacts, tap Edit, and then tap the minus sign next to the source you want to unlink.
You can link two or more contacts with the same name or with different names, such as a personal card and a company card or two partners at the same business, but when you link two or more contacts, only the primary contact appears in the Contacts list and the linked contacts are listed on the contact they've been linked to.
To use a different name for the unified card, tap the name you want to use and then tap the button that reads Use This Name for Unified Card. The names on the individual contact records don't change but the unified card shows the name you selected.
If you make changes to one record, that information syncs with the source it came from but doesn't change on records from other sources. This means if you change the e-mail on a contact in Google, the information is updated on the Google server and on your devices that access the Google server, but it isn't changed on the record that comes from Facebook.