Ha! I came over here to link to that interview, and you'd already mentioned it. Here it is in full, and this is the relevant bit:
the whole point of that scene was that he can't express himself. We never wrote past that, although we did have a long conversation with Matthew Rhys in which we shared some of the details that might be on the other side of it if Phillip could articulate it. Essentially, talk to him about what would be in his semi-conscious mind that he couldn't find the words for.
no subject