Step 1 Write down or copy this Google Calendar URL you want to add to your iPhone. https://goo.gl/89ZgmP
Step 2 Go to the "Settings" on your phone, then scroll down and select "Mail, Contacts, Calendars."
Step 3 Tap "Add Account" and select "Other."
Step 4 Select the "Add Subscribed Calendar" option, fill in the Google Calendar URL in the Server box and click "Next." Change any settings you see fit before saving the calendar. You do not need a username or password.
Step 5 Toggle your view of the subscribed calendar by opening the Calendar app and tapping "Calendars" in the upper left corner. Tap a calendar name to either display or remove calendar events.