Which "cloud" are you using? I use Google, and there is an option to delete from the phone once photos are safely backed up in the the cloud, to free up space on the phone. And I can always download from cloud to my computer too.
If it's another cloud that doesn't offer that option. then download your photos and store them on your computer, an eternal drive, CD or DVD, etc, then delete from your phone; then you can safely explore what happens to the cloud storage (If the photos go away or stay when your phoen syncs again).
With Google, the photos are not so much "synced" with my phone as backed up as I take them and connect to wifi. They automatically get uploaded when I am connected to wifi, so my stuff is always there.