The skimmer is taking in bacteria they die= release of phosphate
Skimmer takes in particles of food,waste, ect.......it breaks down= phosphate
These are just my guesstimations of what happens
I don't think anyone knows what is actually taken up at the point of reaction/frationation........it's all supposition and theory based on what the test numbers read. I know there is an article or two about bacteria counts but I think the value and conclusions are overstated in relation to how to run a reef tank.
I'm curious why are you focusing on such minutiae? Other than for interest and conversation I don't see the value.
Just for fun you should test the water before it goes to the skimmer and the water after........maybe that will give you more answers or more questions
