When you delete photos from your iPhone the cloud copies will follow the synchronisation and also get deleted.
You might get a reprieve via ‘recently deleted photos’
It should be possible to copy photos across to a drive from either the iPhone or the iCloud, and if there are problems such as it refusing to copy more than one or a couple at a time then have a search online for some different example methods.
Photos are also precious to me, but I also take photos of anything and everything, and also screenshots of anything and everything. This means that on occasion that I’m worried about space I can throw away some sacrifices.
If you go to the photos app, and change to ‘albums’ view then some useful categories are listed:
Expect to see ‘recents’ and ‘favourites’, and any albums you’ve created for organising.
But there can be some funnies such as ‘height xxx pixel’, ‘width xxx pixel’ etc. For me these could generally be resized edits I’ve made to save space when attaching to a forum message, so that’s a good place to start browsing for what could be easily deleted
The ‘places’ album gives you a map view of where you took photos (as long as you have location services on)
Many will be important, but if I zoom in on areas then I can look up Tescos for the randoms such as an item that was on special offer which I sent to see if it was of interest - an easy choice to delete
(Note that when looking through albums and deleting you will get asked if you want to just ‘remove from album’ or to fully ‘delete from library’ - delete will of course delete it)
A run through ‘iPhone storage’ can be enlightening about what is used by each app, and then you can choose to delete the contents (such as iPlayer downloads) or which apps could help you temporarily by removing the app for now and reinstalling later