Except that you shouldn't.
What really happens is that as you rotate your left foot clockwise while placing step 4, your left toe now points at or across your right foot, so we say that the right foot is "held in CBMP".
However, as step 5 is placed, the right leg will turn more than the left foot did, so it will exit CBMP.
Some authors such as Hearn would say that the continued rotation of the body will subsequently re-establish CBMP of the right foot, but this is really an abuse of the terminology, as if it applies here it would apply on many other steps with strong CBM that are not traditionally described as being into CBMP. It also violates the "without the body having turned" portion of the traditional definition of the term, since it's precisely body turn that is achieving it.
The whole thing really relates to someone's historical typo or confusion between "held in CBMP" vs placed into CBMP. Once this became part of the party line, dancers who found it wasn't what worked in practice had to invent ever more convoluted theories to reconcile what they did with what they thought they were supposed to say.
But to put all of this in practical terms, what it comes down to is that step four of a spin turn is not really about rotating your left foot while you are on it. Do that and you will have a weak and precarious spin turn, though it's what many who ordinarily dance the step quite well will mistakenly attempt to do when demonstrating "by the book". A better spin turn is danced by turning in the left foot somewhat and placing it slightly off the line of dance, then doing an ordinary "inside of turn" mirroring/accomodating of the movement of the lady's body towards step 5.
) as you begin the step.