The Phoenix crossbow is a quest item used in Shield of Arrav to join the Black Arm Gang. As it is a level 1 weapon, it has stats below that of even a regular crossbow. The Phoenix crossbow has no wielding requirements.
This item can only be obtained from from the Phoenix Gang weapon store.
Upon release of Shield of Arrav, the Phoenix crossbow was tradeable on the Grand Exchange. After complaints that this made the quest too easy, it was then made tradeable between players only.
The crossbow was made untradeable entirely on 13 February 2017, when Shield of Arrav was reworked to allow the quest to be done without having a second player's help.