Hydroxyapatite is the main component of tooth enamel. It contains phosphorus in the form of phosphates, pyrophosphates etc. that are found to exhibit the the property of phosphorescence. But why don't the teeth glow in the dark ?
fJust to add a little more on the interface between optics and dentistry:
Whilst teeth do not phosphoresce, they do in fact autofluoresce.
The differential auto fluorescence of healthy tooth and carious tooth has been used for the early diagnosis of caries. (Gugnani N, Pandit IK, Srivastava N, Gupta M, Gugnani S. Light induced fluorescence evaluation: A novel concept for caries diagnosis and excavation. J Conserv Dent 2011;14:418-22) and (http://www.opticsinfobase.org/boe/abstract.cfm?uri=boe-2-1-149)
To see teeth glow or rather, fluoresce - they should be illuminated with short wavelength light, like blue light (wavelength 450 nm) and the teeth will glow green, which will be visible if the the blue light is filtered out.
Firstly, phosphorus does not exhibit phosphorescence on its own (don't let words mislead you, they often don't mean what they seem like): See http://en.wikipedia.org/wiki/Phosphorescence#Materials and http://en.wikipedia.org/wiki/Phosphor#Standard_phosphor_types
Even if phosphorus did do so on its own, it would not do so in the body because it is always (almost always?) present as phosphate (PO4-), and this again is most often incorporated in other compounds such as nucleotides.