Phosphorus is the Refinement of Phosphorus and is practiced by Prometheans that cannot wait for the Magnum Opus for whatever reason, whether it be having nearly reached it and failed, or their Torment driving them ever-deeper into despair.
The Light-Bringers do not wait. They try every substance, they zoom through everything they do, and react instead of waiting. Though a Promethean cannot taste the sweet ambrosia that is life, the Phosphorus do their best to mimic it. They are the light that guides their fellow Prometheans through the tunnel, even if they burn out in the process.
It is easy to misunderstand the Phosphorus as just thrill-seekers and daredevils that wish to throw their pilgrimage away. But in their madness, there is method; through ephemerality, through the sampling of life's joys, they will flicker out from lead and into gold. They either win big, or lose hard.