'Phoenix' was the code name for an experimental Romulan heavy cruiser. It was thought to have the speed of a D7 class battle cruiser, a size larger than a Constitution-class and about as heavily armed, with Romulan plasma torpedoes.
According to a Starfleet Academy simulation scenario, the Phoenix had not been seen in Federation space but was testing their defenses near the Romulan Neutral Zone and destroyed 4 outposts. The ship was stolen by renegades from the Romulan Star Empire who wished to escape Romulan oppresion and the Federation did not intervene to their plea.
- The Phoenix is also mentioned in the computer database of the Academy outside the simulator, establishing that the ship indeed existed; although the events surrounded it in the simulation could be fictitious.
The Starfleet sent a Constitution to intercept it. According to a Romulan Captain, the Phoenix was controlled by renegades wished to harm the relations with the Federation. The ship caught up with the Phoenix near Clark Colony, and the renegades explained that the Federation is as bad as the Romulans and opened fire. After a dogfight, the Phoenix warped away.
In a later simulation, the Phoenix appeared near Demeter protostar, a protostar near the Neutral Zone which displayed unusual space-time rifts. Both the Starfleet ship and the Phoenix were transported (along with a Tholian starship and a Gorn Cruiser) in a realm controled by the Zy, and put to fight for the simple reason to determine which race is the strongest. Having traced the position of the Zy, Sturek calculated that a Romulan plasma torpedo might destroy their containment field. The Starfleet ship gave directions to the Phoenix and the Zy were crippled by its firepower and transported everyone back. (TOS video game: Starfleet Academy Starship Bridge Simulator)