How to add the calendar directly to your iPhone/iPad
Step 1: Write down or copy the URL for the Google Calendar you want to add to your iPhone.
Step 2: Tap the "Settings" icon, 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.