Accessing the contacts that you store with the most popular email service providers -- including Google -- requires just a few simple mail account setting tweaks on your iPhone. In fact, you can sync all of your contacts from multiple sources with your iPhone and unify any resulting duplicate contact records straightforwardly. But, if Gmail is the most important of them all, then it's important that you also make it your default account. This will ensure that your Gmail captures all new contact information you input directly onto your device going forward.
Step 1 : Tap "Settings" on the Home screen. Next, touch "Mail, Contacts, Calendars."
Step 2: Tap "Add Account," followed by "Google" on the Add Account screen. If you've already added your Gmail account to the iPhone, skip ahead to Step 4.
Step 3 : Type your email address and password in the fields that request them on the Gmail screen. Optionally, type in an account name as well, and replace the automatically generated description with a more memorable or specific one – for example, "Work Contacts," "Builders," or "Family and Friends," then tap "Next."
Step 4: Toggle the "Contacts" switch to the "On" position. The switch should appear green. Touch "Save."
Step 5: Tap "Contacts" on your Home screen. Your Gmail contacts automatically sync to the iPhone.
How to transfer iPhone contacts to Gmail via Settings:
If you intend to export iPhone contacts to Gmail without iCloud, the Settings app could be your choice. Via Settings, you can not only import your iPhone contacts to Gmail but also sync Gmail contacts to iPhone. (The following steps are performed on iPhone 8 Plus running iOS 12.)
Step 1: Go to Settings app on your iPhone.
Step 2: Scroll down to choose "Passwords & Accounts".
Step 3: Click "Add Account" and tap on "Google".
Step 4: Enter the information required to add your Gmail account and click "Next".
Step 5: Once your account is successfully verified, click "Save".
Step 6: Turn on Contacts to sync your iPhone contacts to Gmail, then choose "Save" again.


http://www.gmailinformation.com/blog/how-to-transfer-gmail-contacts-to-iphone/