When I switch my iPhone photos to download and keep originals will it still be saved onto my iCloud

Yes. That option only affects whether some of the photos on your iPhone may be smaller optimized versions. See the following from Set up and use iCloud Photos - Apple Support

If you turn on Download Originals, iCloud Photos keeps your original, full-resolution photos and videos in iCloud and on your device.

Yes. Originals will still remain synced to your iCloud account.

Axel F.