iTunes can be used to sync calendars on Mac and iPhone. However, iTunes calendar sync list gets cluttered with deleted calendars. See for example https://discussions.apple.com/thread/6840043 In order to clean iTunes calendar sync list, check the unwanted calendars, sync, delete them on iPhone. Go back to iTunes, uncheck the unwanted calendars, sync again, and the unwanted calendars should disappear before your eyes. This worked for me with iTunes 12.8.12, Mac OS 10.11.6, iOS 12.1.2.