The Phlogistinator, for the most part, functions in combat like the Pyro's default flamethrower but lacking the compression blast ability and receiving no random critical hits. It trades these features for the ability to power up, similar to the Soldier's Buff Banner.
The Phlogistinator fills up the "Mmmph" meter by dealing fire damage. When the meter is full, the player can unleash the stored energy to activate a crit-boost effect similar to the Kritzkrieg. In the state, the Pyro also gains 90% resistance to all damage. This effect lasts for approximately ten seconds after activation.
This weapon is part of the Dr. Grordbort's Moonman Pack set for the Pyro. However, there is no set bonus for wearing all of the pieces of the set at the same time.