the cable is simply a shielded 3 conductor 22 guage stranded cable using red white black and shield as the forth wire.
it has a rj 11 on one end and a handset 4p4c connector
(handset 4 pin ) on the other end, also erroneously called a rj-9, rj-10, 0r rj-22.
there are no such connectors as rj9, rj10, and rj22.
but they can be found on ebay or the net labeled as such.
the pin outs are straight through.
look at you old connector up close an just match it.
cat 5 cable works ok, but I ordered a 3 conductor shielded cable and hand set connectors and made my own.
cost about 3 bucks total.
hoped this helped.