Phosphorus and chlorine can form various compounds, but the most common ones are:

* Phosphorus trichloride (PCl3)

* Phosphorus pentachloride (PCl5)

The formula P5Cl8 suggests an unusual ratio of phosphorus to chlorine atoms, which is not typically observed in known phosphorus chloride compounds.

It is important to note that the existence of a compound can be influenced by factors like temperature, pressure, and the presence of other reactants. However, the formula P5Cl8 has not been reported in the scientific literature, making it highly unlikely to be a known compound.