from what i know, any photo you delete on your device deletes it from iCloud as well. There is a "recently deleted" album in your photos app, though, if youre running iOS 8 or above (i think its 8). might be worth looking there
The above poster is correct. Once you've deleted them from the phone they will also be removed from iCloud. Check in the Photos app for recently deleted photos. If it's been longer than 30 to 40 days they will not be in the recently deleted folder any more.
Check the recently deleted folder, if it's 30 days after you deleted the photos, you might need to use 3rd party software to recover them. So, backup some important files is really necessary!