To sync calendars from your Mac to your iPhone you can ether use iCloud or just the regular sync.
To just do regular sync, plug your iPhone to your Mac and click on iPhone. Then go to info and click sync calendar.
To use iCloud, on your iPhone go to Settings > iCloud > toggle on calendar.
To use iCloud on your Mac go to Preferences > iCloud > toggle on calendar.
You're set, calendars can now be synced with iPhone and Mac.