1. Login to your FullContact account and connect a Google Contacts account and set it to Sync with Unified Contacts under the Sync Settings page. Click here for a guide on how to connect a Google Account to your FullContact account.
2. Go to your Android Device Settings and find the Accounts & Sync page. Once in the Accounts & Sync page please connect the Google account that you connected to your FullContact account and set that account to Sync Contacts. This will enable all your Google Contacts to sync to your phone native Contacts.
Now every change to make to your Unified Contacts in FullContact for Android will sync back to Google and your Device Contacts through Google.
Please note that if you have set multiple accounts in your Device Settings to sync Contacts this will create duplicate contacts in your Device Contacts App as the contacts will be pulled from multiple sources that may not sync with FullContact so to resolve this issue we suggest only syncing one Contacts source in your Device Accounts settings.