1. Tap the "Settings" icon on your iPhone
2. Tap "Mail, Contacts, Calendars" "Add Account" and click "Other"
3. Choose "Add CardDAV Account"
4. Fill in your account information for Google
- Server: google.com
- User Name: your full email address.
- Enter you password for Google password for Isla.
- Add an description (e.g. Isla Contacts).
5. Click on "Next."
6. Please make sure your "Contact"s option is turned on. To do so, click on "Isla Contacts" and verify that the account is turned on.
Once you're done setting up CardDAV, open the "Contacts" app on your iPhone, and syncing will automatically begin.
For more on this, please visit Google's support for CardDAV.