1) Surface area - The larger the surface area, the larger the area for intermolecular bonds to act upon so the stronger the forces experienced are.
2) Number of electrons - The more electrons a molecule has, the stronger the intermolecular bonds.
Phosphorus has 15 electrons whilst Hydrogen has only 2. This means that the forces exerted will be much lower. Furthermore, Phosphorus is of a lower period and thus has more electron shells so will have a larger surface area for intermolecular bonds to act upon. Therefore, both of these factors mean that the intermolecular bonds are much stronger between phosphorus molecules than hydrogen molecules. Hence, more energy must be supplied to break these bonds, meaning that melting and boiling point of Phosphorus will be significantly higher.