Sal says that her story is hidden behind Phoebe’s. What does she mean by that?

Sal draws an analogy between Phoebe's story and an old brick fireplace uncovered by her father on the night her mother left. Sal's father had gradually chipped away at a plaster wall in the farmhouse until he made his unexpected discovery. Just as the old fireplace was hidden behind a wall, so Sal's story is hidden behind Phoebe's. What Sal means by this is that her own story is intimately related to that of Phoebe....

Sal draws an analogy between Phoebe's story and an old brick fireplace uncovered by her father on the night her mother left. Sal's father had gradually chipped away at a plaster wall in the farmhouse until he made his unexpected discovery. Just as the old fireplace was hidden behind a wall, so Sal's story is hidden behind Phoebe's. What Sal means by this is that her own story is intimately related to that of Phoebe. The memories that she has of Phoebe will always be there, never to be forgotten. At the same time, though, Sal can choose to build her own life, just as someone once built a wall over the old fireplace. It's her own life, but it wouldn't be possible for her to build it without the foundations provided by her relationship with Phoebe.