ChemGlobe: Phosphorus: Electronic, thermal, and steric data along with basic information.
ChemicalElements.com: Phosphorus: Basic information, atomic structure, and table of isotopes.
EnvironmentalChemistry.com: Phosphorus: Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Phosphorus: Basic physical and historical information.
LANL: Phosphorus: Properties, handling, production, and uses.
Lenntech: Phosphorus: Physical data, chemical properties, health and environmental effects.
Phosphorus: Data tables and historic information.
Radiochemistry of Phosphorus: Full text of the monograph by William T. Mullins and G. W. Leddicote (Oak Ridge National Laboratory, Oak Ridge, Tennessee). [PDF]
Visual Elements: Phosphorus: Image, general and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Phosphorus: Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Phosphorus: Properties of the element, including its history, applications, and characteristics.