50 years ago, phantom pain was blamed on misfiring nerves 

Physiology of the phantom limb — Science News, May 11, 1974 

Nearly everybody who has had a leg or arm amputated sometimes experiences the sensation or feeling that they still have their missing limbs. Some of them experience pain in their “phantom limbs.” … One assumes that [cut nerves] frequently fire off impulses to the central nervous system and … create the sensation of a limb still being present…. [Scientists] have now confirmed that these events occur, at least in experimental animals.

Update

The cause of phantom limb pain is more complicated than just mis­firing nerves. Post-amputation changes in the spinal cord and brain may also contribute, mounting evidence suggests. Therapies such as pain relievers and using visual feedback from mirrors to trick the brain can offer some relief (SN: 03/02/14). But researchers are still searching for more effective treatments. In 2019, scientists reported that electrically stimulating nerves near amputation sites not only helped two men detect pressure and motion through a prosthetic leg, but also reduced their phantom pain (SN: 09/09/19).