Nodes are the essential building blocks in the Advanced interface to the Poser Material Room. They are the graphical representation of mathematical function calls, that is: calculation procedures which turn parameters (inputs) to a result (output).
All nodes in the Specular group respond to specular light, which refers to specular light from direct (point- spot- infinite) sources only. The regular ‘specular’ node itself, either separate or embedded in the PoserSurface definition directly is fast to calculate, but falls short for a neat illusion of about any real stuff except hard plastic.
B.T. Phong introduced (in 1973) a method to make neat highlights and smooth surfaces out of a surface which consisted of small flat elements, as our 3D objects do.
As his method was improved by Blinn, and as the results in Poser hardly differ from the regular specularity (left pawn, vs right pawn showing Phong):
the method – and the node – can be considered outdated. The parameters have the same meaning as the Specular ones.