At the end, what is Phillip studying?

I think that this question is asking about events at the very end of the novel. In my text, this information is found on the last page. The final chapter of the book moves quickly. When the chapter starts, Phillip is still stranded on the island. He is rescued by a naval destroyer that just happens to put crew ashore on the small cay. Phillip is rushed to a hospital in Panama, his mom and dad arrive, he is moved to a hospital in New York for a series of eye surgeries, his sight is restored, and he and his family return to Curacao. The war ends, and Phillip's family moves again. It's not until after all of that happens that Phillip tells his readers that he has "spent many hours" looking at and studying charts of the Caribbean. We are told that he has found many islands in the area, and Phillip has even found the Devil's mouth. Presumably, Phillip is looking for the small cay that he and Timothy survived on for all of those months. Phillip's goal is to go back to the island and visit Timothy's grave.

Someday, I'll charter a schooner out of Panama and explore the Devil's Mouth. I hope to find the lonely little island where Timothy is buried.
Maybe I won't know it by sight, but when I go ashore and close my eyes, I'll know this was our own cay. I'll walk along east beach and out to the reef. I'll go up the hill to the row of palm trees and stand by his grave.
I'll say, "Dis b'dat outrageous cay, eh, Timothy?"