Open the Google Calendar app on your iPhone
Tap the menu icon
Scroll to the calendar you want to share
Tap the calendar name
Tap Settings and sharing
Tap Add people or groups
Enter the email address of the person you want to share with
Choose the permission level
Tap Send
If needed, use a web browser on your iPhone and open Google Calendar
Sign in to your Google account
Open Calendar settings
Select the calendar you want to share
Add the person’s email address
Set the sharing permissions
Save the changes