A diary entry is an account of your own personal thoughts and experiences. To write a diary entry in the voice of Phillip from Theodore Taylor's The Cay recounting the moment he became afraid for Stew Cat's life, you first want to describe the moment when Timothy began suspecting Stew Cat is a jumbi. Think about what Timothy and Phillip had been doing the moment Timothy brings up voodoo and what had happened just prior.
For example, Phillip and Timothy had just had dinner when Timothy begins grumbling that still no aircraft have flown overhead and blaming it on a jumbi. Prior to that, as Phillip explains, it had rained the night before, which gave them plenty of drinking water and left them feeling hopeful--they felt like their luck was starting to change. So, as Phillip continues to describe, that day, they "did their chores with one ear to the sky, listening for the sound of engines" (p. 81). As a result, when they still heard no engines, they felt even more disappointed than before.
Next, you want to describe Phillip's reaction to Timothy's reference to voodoo and the speculation that Stew Cat is a jumbi. Reflect on from whom Phillip learned about voodoo and what he knows about it. You may even want to do your own research on voodoo to explain what a jumbi is. Think about why Phillip would think voodoo was ridiculous. Especially try to further explain why Phillip would say in his narration, "Voodoo is silly, I knew, but it was also frightening" (p. 82). Why would Phillip think voodoo is frightening?
Finally, describe the moment you, as Phillip, wake up the next morning to discover both Timothy and Stew Cat missing. Describe what actions you took to try to locate Stew Cat, such as circling around the island using your cane, finding Timothy and hearing him be evasive in answer to your questions about where Stew Cat is, and beginning to fear for your own life so much that you try to find the raft but can't find it. Be very descriptive about your emotions as you relay going through these activities and discoveries. Think about the types of sensations we have when we're afraid such as sinking feelings in the pit of our stomachs, heart palpitations, and sweating. Try to use these sorts of descriptions to help your reader understand your feelings of fear and why you were afraid.