A phantom limb is a reality in an amputees mind. Evaluate a different situation where a reality only exists in a persons mind. Have you every experienced a reality that only existed in your mind?
An example would be when a person has experienced an euphoria situation and that situation is taken away from that person. The person would feel the nostalgia afterward when he experienced a similar situation in the future. A good example would be the joy of going to the beach. The smell of the ocean and the scenery can be triggered inside the person’s brain when he does something that even have a slightly connection to the joy that he has experienced from going to the beach. So whenever the person sees salt water, he would be reminded of the time he went to the beach and it would triggered the scenery inside his brain.
My own personal experience is when i dislocated my shoulder and the pain was unbearable. so whenever something happened to my shoulder, a cruciating memory of the incident appeared inside my mind. And it just flicks back to the memory of being in pain. the vivid memory lasted a while because the incident was too much for my brain to compansate. So whenver i do something that put a strain to my shoulder, it reminds me of that incident.