There are many reasons that people get swelling (edema) in their feet and legs. Since your dad's feet don't seem to be getting better after cutting down on his salt intake, and elevating his legs, I would call the doctor to let him know. The fact that your dad's feet are red concerns me, as this can indicate an infection. I would at least call his doctor with this uptake, especially as he knows your father's medical history and might be able to help you over the phone. It could be a matter of continuing the low-salt, elevated feet regime for longer. But I suspect your dad's doctor will want to see him to plan the next steps.