Read about allotropes and polymorphs, about gamma P4 and visualize the structure with an interactive applet, read about fibrous red phosphorus and visualize the structure with an interactive applet, and read about semiconducting black phosphorus and visualize the structure with an interactive applet.
Here are lecture notes, and here are lecture slides.
Here you can learn about spherical aromaticity and examine the interactive molecular orbitals of P4.
Further resources: (i) a reading on the Early history of phosphorus, (ii) a paper on the Molecular and Electronic Structure of AsP3 and P4, and (iii) supplemental exercises.