Trouble with importing photos from iPhone to Mac when I have enabled iCloud Photo Library and selected "Optimize iPhone Storage"

I’m not sure I can address everything in your post, but here are some things that might help narrow down some options.

• If you have “optimize photos” on your iOS device/iPhone - then it is designed to upload the full, original images to iCloud. Full stop.
• Then you are expected to download those photos to all other devices from the ful version in iCloud.
• At best - you always get the perfect version and the downsampling only happens to the local / non-permanent copy that’s on a device with low storage space internally.
• At worst - you fill up the iCloud space and have to buy more to store all the originals - and you still retain the full size versions online, but at a cost.

Depending on where you split from this general idea - you may or may not have some issues that I didn’t anticipate, but I would probably reach out to Apple Support to verify your iCloud is correct and full and see options to get everything from the phone to iCloud, everything from the Mac to iCloud and then sort out the options.

Getting the local cached copy from the iPhone is very against the design so I would think you’d need specialized skills or software much more involved and time consuming than just fitting into the intended use pattern.

After some days of researching, here is the solution that works for myself the best.

Recap of the my situation (the applicable situation) : I use iCloud Photos Library. The iCloud storage is 200GB and becomes full after 1~2 years of usage. I have a 4-bay Synology NAS with RAID 0 enabled, and several large portable hard drives, and I also use Google Photos (unlimited space) and Amazon Cloud drive (Prime Photos, also unlimited), so I trust my ability of safekeeping the photos and don't want to spend extra money on iCloud storage.

Steps:

1. I created a new Photos library on my Mac and enabled iCloud in preference. So it downloaded all the photos from iCloud to my Mac.

2. On Mac, add all photos to a new album called "backed up on ". This new album will get sync'd to my iCloud and my iPhone. After that I will disable iCloud for this library on Mac.

3. On my iPhone, use an app called "Mass Delete" (free) to delete all the photos older than 6 months.

4. (Optional) for photos older than 6 months and I want to keep a copy on my iPhone, use AirDrop to copy them from Mac back to my iPhone.

5. Several months later, when my iCloud storage is full again, I delete all the photos in the "backed up on " album on my iPhone.

6. Another several months later, when my iCloud storage is full once again, I will start over from step #1.

The pros of this solution:

1. I always have photos at least up to 6 months old on my iPhone/iCloud all the time. I never have to empty it.
2. Imported photos don't overlap, or in other words, there are no duplicates on my Mac.
3. I can still take full advantage of iCloud Photos Library and the "Optimize iPhone Storage" feature.
4. I don't need to use Photo Stream.
5. I don't need any other 3rd party software to do the import. Most of the photos imported to my Mac has the latest organization and edition as they are before they get deleted.

Cons:

1. Overtime my photos will be scattered in multiple Photos libraries. But I am fine with that.
2. For the 6 months of photos in the "backed up on " album, they may get out of sync between the iPhone/iCloud version and the Mac version if I edit them. But I don't edit photos often so I can live with that.
3. Step #3 requires a 3rd party app. There are possibly other ways to do this time-filtered delete using the built-in software.