Syncing iPhone with new HD on Mac after Time Machine restore

I tried posting this yesterday, but got in a tangle with my iPhone on which I was typing, and ended up with two fragmentary posts. I apologise, and am trying again.

The hard drive of my Mac mini started failing and I am having a new one (a solid state one, actually) installed by an authorized Apple repairer. When I get it home I shall restore the contents from a Time Machine backup.

My question is this: I sync my Mac with my iPhone via iCloud. During the few days while my Mac mini has been out of action, I have had to add some dates to Calendar on my phone. When I have restored the contents of my Mac’s HD and I connect it to the Internet, syncing will start automatically. How can I ensure that it is the up-to-date Calendar that is synced from phone to Mac and not vice versa?