Upgrading to a new iPhone could be a tiresome event. You have to re-install all the apps and so much syncing has to be done. The most painful job is to save all the contacts one by one (in case you don't have a backup).
While a few services like iCloud allows you to take a backup and retrieve data whenever you need, apps like Facebook can also help you serve the purpose. All you have to do is to sync the contacts. That said, you won't be able to add new contacts other than the ones on your iPhone, you can just update the information of existing contacts.
While it is possible to add new contacts from Facebook on an Android phone, it's just not possible on an iPhone, thanks to Apple's tight security rules.
Here's a step by step guide to help you out in syncing your iPhone with Facebook contacts.
Step 1: Open Settings
Unlock your iPhone and head straight to settings
Step 2: Open Facebook
In the settings page, scroll down until you see the Facebook app and tap on it.
Step 3: Enter Facebook credentials
Now, quickly enter the Facebook credentials and hit on the sign in option.
Step 4: Turn on contacts
On logging in, you'll see two toggles - contacts and calendars. Turn on the contacts toggle.
Step 5: Click on update all contacts
After turning on the contacts toggle, click on the update all contacts to start syncing your iPhone contacts with the Facebook contacts.
Quick Tip: If you want to add new contacts, please request for the same personally on Facebook and whenever the other person shares their contact, your contact list will be updated automatically.