Q: turning off automatic syncing between iPhone and Mac

Hello eriiyam,

Welcome to Apple Support Communities.

It sounds like photos are missing from your Mac after deleting them from your iPhone, and you want to know how to prevent this from happening again. The article linked below provides a lot of great information about iCloud Photo Library and it will walk you through the process of disabling iCloud Photo Library on one of your devices.

Get help with your iCloud Photo Library - Apple Support

How do I turn off iCloud Photo Library on just one device?

To turn off iCloud Photo Library for a single iOS device, go to Settings > iCloud > Photos and turn off iCloud Photo Library. 

To turn off iCloud Photo Library for a single Mac, go to System Preferences > iCloud > Options next to Photos, then deselect iCloud Photo Library.

If you have Optimize Storage turned on, you might not have all of your original photos and videos on your device. To download the original photos and videos on your iOS device, go to Settings > iCloud > Photos and select Download and Keep Originals. On your Mac, open Photos, choose Photos > Preferences, then select Download Originals to this Mac. Then you can turn iCloud Photo Library off. You can also select the photos and videos that you want to download from iCloud.com.

The article also describes how pictures in the iCloud Photo Library are deleted and how they can be recovered.

When you delete a photo or video from your Photos app, it will also delete from your iCloud Photo Library and iCloud storage. You can recover your photos and videos from the Recently Deleted album for 30 days. 

Cheers.