Phosphorus can have both a positive and a negative valency.
If phosphorus combines with a metallic element it has a negative valance. The phosphorus because it has a higher electron negativity than the metals will act as an oxidizer taking electron away from the positive metals. This creates a valance of -3
If phosphorus combines with a non metal element with a higher electron negativity than phosphorus it will have a positive valance.
When phosphorus combines with Oxygen to form an phosphate ion it has a charge of +5
Phosphorus can have either a positive valance or a negative valance depending on what other element it is combining with and the relative electron negativity of the other elements.
Phosphorus has neither a positive or negative valency.
Valency is the number of