Phosphorus acid

There are several phosphorus acids. They are acids that have phosphorus in them. Three of them are common.

Hypophosphorous acid, phosphorus in oxidation state of +1, salts are called hypophosphites, reducing agent
Phosphorous acid, phosphorus in oxidation state of +3, salts are called phosphites, reducing agent
Phosphoric acid, most common, phosphorus in oxidation state of +5, salts are called phosphates