Phosphorus does not have a formula, in its pure form it is an element which contains only atoms of Phosphorus and nothing else. The chemical symbol for Phosphorus is P.
Added:
is the adjective of compounds related to the phosphiteanion: PO33-
or to the acid H3PO3 , phosphorous acid.
Formula: P4
The chemical symbol (not formula) of phosphorous is P; the chemical symbol (not formula) of chlorine is Cl.
Also phosphorous is the ion (PO3)3-.
Formula: PCl3
You think probable to the unstable compound P4S2.
Formula: P2O3
The formula (symbol) for aluminum is Al. The symbol for phosphorous is P. The formula for aluminum combined with phosphorous is AlP (aluminum phosphide).
P4Se3
Phosphorous Hydride = PH3
Phosphorous Trioxide
PCl3
Phosphorus pentachloride is a chemical compound with the formula PCl5.