If you can disconnect the computer from the network quickly enough, you may be able to export the photos in question to a temporary location outside of the Photos library, then reload them after the deletion happens. They will then to back up to iCloud and back to your phone.
Just to be clear, the choice is between deleting on all devices and not deleting anywhere. There is no option to delete from only one device among those linked to an iCloud Photos library.
The whole purpose of iCloud Photos is to keep the libraries on your devices in sync with each other using iCloud Photos as the central coordination point. Add to one = add to all; edit on one = edit on all; delete on one = delete on all.
If your iPhone has too little storage to handle your entire iCloud Photos library, you can use the "Optimize iPhone Storage" option, which can trade capacity for speed of access when you need the full resolution of a photo for editing or viewing details.