Zooey is the Glass brother who is (most concretely) responsible for helping Franny to resolve her spiritual crisis. Though he does send her into tears at first, this tough love is probably a necessary step on the way to the story's climax (Franny has to hear these things, even if she really doesn't want to). Of course, Zooey's final words of wisdom over the phone are what catalyze Franny's resolution and even become the novel's conclusions about spirituality and love. In this way, Zooey guides the text itself or even the reader as well as his fellow character.
Buddy is a guide in a few different ways in "Zooey." First, as the author of the story, he is literally guiding the action and crafting the characters. He has the final say in who Zooey and Franny are, at least on the written page. But his presence is felt within the context of the story as well, not just as its somewhat masked creator. His letter dominates the first quarter of the story. In addition, his influence has clearly played a large part in determining (for better or worse) the man that Zooey is. Buddy returns again at the end of the story, not through a letter but again filtered through Zooey, this time as a fake persona over the phone. It is in some ways Buddy – in addition to Zooey and Seymour as well, – who guides Franny to her resolution.
Just as Buddy acts as a guide over the phone to Franny without actually being there, so Seymour guides both Franny and Zooey despite having been dead for seven years. Zooey's memories of Seymour, as well as the objects in Seymour's room and his diary entry, prompt him to speak with his sister Franny. And it is Seymour's story of the "Fat Lady," albeit it told through Zooey, that gets through to Franny and directly leads to the resolution of her crisis and the story's plotline.