How to fix Mac calendar not syncing with iPhone 1. Turn off iCloud Calendar and turn it on again
If you are unlucky to encounter Mac calendar not syncing with iPhone like said above, you can refer to the fixes below to troubleshoot. Generally speaking, as long as you have turned on iCloud for calendar and sign in the same iCloud account on all your iOS and OS devices, including iPad, iPhone, MacBook, iMac, the calendars will be synced among the devices automatically without any error.