Hello sheetsfamily4,
Welcome to the Apple Support Communities!
I understand that you would like to delete some photos off of the Photos application on your iPhone, but do not want to lose those photos from your computer as well. In this situation, I would recommend reading over the Download photos or videos to your computer section in the attached link. Once erased from your phone, after downloading to your computer, the photos will be removed from Photos on the iCloud website, but will still be stored in the location you choose on your computer.
Use the Photos app on iCloud.com - iCloud Help
Have a great day,
Joe