How do I delete photos from my iPhone but keep them on my Mac

Mynne wrote:

1 - if I turn off iCloud I can then delete all photos in my phone? They will stay on my Mac?

2 - after doing so when I turn iCloud back on will the photos stay on my Mac or will they pop back onto my phone?

1 - yes, the will stay on your Mac.

2 - as I don't use iCloud Photos I'm not sure if after you turn on iCloud again if the photos will be deleted from the Mac or added to the iPhone. I'm thinking deleted from the Mac.

If you want to keep a set of full sized photos do the following:

1 - on an external drive formatted either APFS (GUID partition) [for an SSD] or OS X Extended (journaled) [for a rotational HDD] create a new, empty Photos library.

2 - set the library to be the System Photos Library and enable iCloud Photos. DO NOT ENABLE "OPTIMIZE MAC STORAGE".

3 - let the download begin. I could take up to a week depending on the size of the iCloud Library.

4 - when the download is complete disable iCloud Library on the EHD library and set your library on you internal drive to be the System Photos library.

This will give you a Photos library with all of the full sized photos.

NOTE: if you do not have Optimize Mac Storage enabled on your Mac's Photos Library you can just copy the library to the external drive for a full backup. If you do have optimize enabled you'll need to do what's in steps 1 - 4.

Please read the following user tip and restate your question/problem in detail: 

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Do you have iCloud Photos enabled?

You would have to stop using iCloud Photos as that is a syncing feature and any deletion your do on one device will be duplicated on the other device.