Open Google Calendar on your iPhone
Tap the menu icon
Scroll to the calendar you want to share
Tap the three dots next to the calendar name
Tap Settings and sharing
Tap Share with specific people or permissions
Tap Add people
Enter the email address of the person you want to share with
Choose the permission level
Tap Send
To share a calendar link, open the calendar settings
Enable public sharing if needed
Copy the shareable link
Send the link to the person you want to share with