Sync my calendar data from iPhone to iCloud. Which overwrite first?

I installed the new OSX, but I had some problems with time machine.

I need to sync my calendar data from the iPhone to iMac, through iCloud.

But iCloud has a lot of events that I want to remove before I sync, because I do not know if iCloud will overwrite the ones in iPhone

I tryed to delete everything in the iCloud, but saids a problem with server cannot delete the calendar events. I created a new calendar and tryed to delete the old one which have a lot of events. But no luck.

Can anyone help to understand how iCloud works. Which data is overwrite first ?

In my case the most recent data, is the one in iCloud . so I think this data will overwrite the one in the iPhone, and I do not want that.

Thank you in advance