how do i view icloud photos on my HP desktop and then download to desktop

You can use any internet browser and log into www.icloud.com and go to the Photos app there to view iCloud Photos. You can also select and download photos using the Internet browser.

Another option would be to install and use iCloud for Windows. See information in Set up and use iCloud Photos on your Windows PC - Apple Support

Do you have Optimize Storage turned on for iCloud Photos on your iPhone? See the information in Set up and use iCloud Photos - Apple Support

That is enough to ensure free space on your phone in most cases.

If you need more help I won't be available until tomorrow. I'll check back then or someone else here might jump in.