From: Chuck on
Non amputees (doctors and such) car theorize about the causes of phantom
limb pain all they want. I think real amputees need to report their actual
experiences in a more revealing way to help everyone understand.

Something happened to me last night regarding phantom pain that I just
wanted to float around out there in cyberspace. What happened to me was
that for the first time ever, I was able to repeatedly cause severe phantom
pain in my missing toes "on-demand." I did this ten times in a row just to
prove that I was causing it using pressure from my own movements.

Last week I hurt my back and one of the disks between my vertebrae was
slightly inflamed. Last night when I went to bed, laying on my back, I
decided to stretch my back out by slowly pulling my knees toward my chest
one at a time. I was very surprised that each time I pulled my
non-amputated leg toward my chest I got a very sharp (phantom) pain in my
non-existent toes of my amputated leg.

This confirms to me this means that actual pressure on a spinal nerve (not
just the nerve endings in the residual limb aka stump - see Neuroma) can
cause phantom pain.

Definition: http://en.wikipedia.org/wiki/Phantom_pain (also references to
using a "mirror box")

From: Chuck on
I found some confirmation of this here:
http://www.caringmedical.com/condition_details/Phantom_Pain.htm