What is Phillip's father's job at the refinery?

Amazon lists The Cay around a fifth grade reading level.  Keep that in mind when trying to figure out what Phillip's dad does at the refinery. The book simply doesn't go into that much detail about what exactly he does.
Chapter 1 is the best place to look for information regarding Phillip's dad and his job. Based on this chapter, readers can assume that Phillip's father is not a manual laborer at the refinery. He's probably not working with pipes and wrenches at all. Readers can assume this because we are told that when Phillip's family lived in Virginia, his father was in charge of building a new refinery.  

It was very different in Virginia where my father had been in charge of building a new refinery on the banks of the Elizabeth River. 

Phillip's father must be very good at his job because his expertise in the field of gasoline production and refineries is what brought him to Curacao in the first place. He was loaned from his company in Virginia to a Dutch company on the island.

Royal Dutch Shell had borrowed him from his American company because he was an expert in refineries and gasoline production.

That's all of the detail that readers get regarding his job at the refinery. Based on that information, I would say that he is an engineer of some kind in charge of the production and design of the refinery.