You can always choose to turn off the Facebook contact syncing on your phone so that your phone goes back to just having the contacts you have entered on it. We have an article on using Facebook and Twitter in iOS and it can provide some insight on this matter:
These last paragraphs in the article might be the most useful parts of the article for your specific question:
You can update your existing contacts with Facebook and Twitter information and photos. Tap Settings > Facebook and Settings > Twitter and then tap Update Contacts. Contacts are matched using email addresses, and contact cards are updated with Facebook and Twitter user names and photos.
Note: Using this feature will replace existing photos with the one your contact is using for Facebook or Twitter.
Sync contacts and calendars
iOS can sync your Facebook contacts and calendars with your device. This feature is off by default, but you can enable it in Settings > Facebook after adding your account.
You will basically want to navigate to those settings and flip the switch for contact syncing in Facebook from "ON" to "OFF."
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