This is what Booker says: in this stage, the hero (the person who gets to be reborn at the end) is "frozen" in an "isolated, imprisoned state." He's fallen under the "spell" of the "dark" sides of his own personality. Sounds like our narrator. When we first meet him, he's grouchy, jealous, and a little angry. He's full of all sorts of ludicrous assumptions about blind people. He's frozen and isolated by his emotions and assumptions.
The narrator rises to the occasion when Robert arrives. With the aid of cocktails, his grumpiness recedes, just like Booker says it's supposed to. The narrator keeps his assumptions to himself, and seems genuinely concerned with making Robert feel comfortable in every way.
Booker says that in this stage the darker aspects of the hero's personality return with a vengeance, locking him "in a state of living death." We have to stretch a little to see the narrator as a typical Booker hero in this stage. Even if you think that smoking marijuana. drinking, and/or watching TV are harmful or a waste of time, you probably didn't think "state of living death" when you read the after-dinner scene. There is more of a sense of sleepiness, intoxication, and fullness than a sense of danger and peril. On the other hand, we learn that this is basically what the narrator does every night. Being locked in the monotony of his nightly routine contributes to his state of dissatisfaction.
But, we still can't quite fit him neatly into the mold of the Booker hero. After all, tonight his routine is being shaken up. Robert is in the house, and he's enjoying his company, even though he's still afraid of Robert. This seems more like an extension of the recession stage than an imprisonment stage.
In this stage things are supposed to get so bad that the hero has little chance of triumphing over his inner monsters. In the Falling Stage we identified some of those monsters – grumpiness, jealousy, making too many assumptions. In the imprisonment stage we added his inability to break from his tired routine to the list. None of those qualities intensify in "Cathedral." They are worst at the beginning, and grow steadily weaker as the story progresses. Instead, a new monster arises – the failure-to-communicate monster. In trying to describe cathedrals to Robert, the narrator finds that words are not enough.
Hmmm. Maybe that monster isn't so new. The narrator is clever, and he can get his point across, but he doesn't exactly communicate positively. He seems to have trouble communicating in general. Maybe he fits the Booker hero in this stage better than we thought. Allegorically speaking, if he can't find a way to describe the cathedral to Robert, he might never be able to communicate effectively with anyone, least of all his wife.
Booker says that in this stage the hero experiences "a miraculous redemption" usually with the aid of a young woman or child. Robert is neither young nor female, but he gets the job done. By showing the narrator an entirely new way of "seeing" and communicating, Robert helps free the narrator from his stagnant vision. He shows him that with creativity and open-mindedness, big and small problems can often be solved. We don't know if the narrator is really reborn, that is, if the effects of his experience will be permanent, or not. But we are free to speculate.