The IUPAC recommended name for phosphorous acid is phosphonic acid.  Correspondingly, the IUPAC-recommended name for the  ion is phosphonate. In the US the IUPAC naming conventions for inorganic compounds are taught at high school, but not as a required part of the curriculum. A well-known university-level textbook follows the IUPAC recommendations.  In practice any reference to "phosphite" should be investigated to determine the naming convention being employed.