If I save my photos to iCloud, can I delete them off of my device and have them still remain in iCloud?

You are correct. iCloud Photo Library is just an extension of the photos on your phone so anything deleted from the phone will be deleted from iCloud photo library as well. It's more for continuity amongst all Apple devices.

iCloud is not a storage service, it is a syncing/sharing service. So, if you are using iCloud Photo Library to upload photos from your device to iCloud, then you are sharing that library with your iPhone, and any changes you make to it will be made to the Library itself.

So, if you delete photos, they will be deleted from the Library.

If you want to archive your photos so you can remove them from your device, you can turn off iCloud Photo Library on your device and start importing your photos to your computer:

PHOTO IMPORT IOS TO MAC/PC

Or, you can upload them to an archival cloud service like Dropbox, Google Photos, Amazon Photos, Flikr, etc.

The purpose of iCloud Photo Library is to have a library that is shared between all devices and computers, with complete access to that library. That access allows you to make changes, edits, additions, or deletions that will affect that library across all devices and computers using iCloud Photo Library.

Cheers,

GB