'Portrait: Theory' came out in '81. It was one of an excellent short 'Theory' series published by Lustrum Press. I don't know how many there were altogether, but I have Portrait, Landscape, Darkroom and Darkroom 2.
Bare details from the book:
Philip's memory is correct regarding the details, though I can't find a specific mention in the book of the make of camera. He does say that he did not bracket exposures, and that he didn't do his own printing. He used semi-matte Ilfobrom or, for dark-skinned people, the warmer-toned Portriga Rapid.
He only owned two lenses: an 80 mm and a 150 mm. He considered the 80 to produce too much distortion, and liked having a lot of space between himself and the sitter - so much so that they often couldn't hear his quiet voice.
He learned about lighting by buying a couple of Lowell quartz lights and doing still-lifes. He preferred daylight over flash and tungsten, but was happy to use all three, and found switching between them to be a good thing.
The '79 portrait of William Burroughs in his loft was taken using tungsten lights. RM remarks that using tungsten had taught him to create strong shadows artificially, and that he wouldn't have had such a strong shadow with daylight or tungsten.
The '78 portrait of Patti Smith holding her neck brace was also lit by tungsten, and RM adds that it was shot at f/16 - the aperture he liked to use.
The '80 portrait of Jennifer Jacobsen holding her breasts was printed with a stocking over the enlarger lens.
The '80 portrait of John Ford (painter) in the bath was also tungsten.
The '80 portrait of Claudia Summers was taken with a single strobe bounced off an umberella.
The '80 portrait of Terry Beans was made with two strobes.