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.
When the Grand Exchange was released, the crossbow could be traded on it. However, this led to complaints that it made the Shield of Arrav quest too easy, so trading was restricted to between players only. The crossbow was made untradeable on 13 February 2017, when the quest was reworked to allow the quest to be done without having a second player's help.