They probably have been interrogated by LE. Maybe that is why CB fears it again. I mean, idk, but i wouldn't be surprised if that happened.
I'm going to watch the episode soon. As for Dr. Phil, he does have the education and, i think, he used to practice. But, after becoming a media personality, is no longer licensed to practice. I have only watched a few episodes of his over the years and I think they really vary depending on the subject. I don't have TV service either, so this is mostly from years ago.
Idk if anyone can be called a "human lie detector". That seems like an oversell even if the person is very, very good at detecting lies.
ETA: the last one i watched was when he had the Schofields on, they're the divorced parent of the so-called "childhood schizophrenic" Janie Schoefield (who does not have schizophrenia, also it is impossible to have schizophrenia as a young child because it requires a certain level of brain development). He had her on when she was a child as the "child schizophrenic". That is a terribly sad case.