INTJ would be Melancholy Choleric (the Choleric is what adds the N).
A Phlegmatic's "observation" (which is described in the APS) is basically their "ambiversion". They are slow to either express, or avoid, so they observe, and again, can "take 'em or leave 'em".
ISFP would be Phlegmatic Sanguine (The Sanguine is what adds the S).
In all cases, the second temperament, the conative (Keirseyan) one, is what connects with S/N. The first temperament (social or Interaction Style) is "blind" to S/N.
The pure Phlegmatic, again, might seem to be inbetween in all the factors, but would likely edge out in favor of INFP. Or, hypothetically, it could be any type, but the basic descriptions seem to be compatible with INP and NF.