You sync your iPhone to your Mac’s calendar following the steps outlined by this link but only the last 30 days appears. How do you extend the period to show a longer period?
Fortunately, there’s a simple fix that involves a minor change in your iPhone Settings. On your iPhone, go to Settings > Mail, Contacts, Calendars, and scroll to near the bottom of the screen until you see Sync. Click Sync and change it from Events 1 Month Back to another menu option, such as All Events.