From what does Phillip learn that Madeline suffers?

It is believed that Madeline suffers from catalepsy.

"A condition characterized by lack of response to external stimuli and by muscular rigidity, so that the limbs remain in whatever position they are placed. It is known to occur in a variety of physical and psychological disorders, such as epilepsy and schizophrenia, and can be induced by hypnosis."

http://www.thefreedictionary.com/cataleptic

These symptoms are very similar to the ones exhibited by Madeline in the story.