A "totem pole" is a large wooden pole with shapes of heads cut into it. The heads are stacked on top of each other. Totem poles were originally carved by native tribes in the northwest region of North America.
These days, it's common for people to compare a business organization to a totem pole. The person in charge is "at the top of the totem pole", and ordinary workers are "at the bottom of the totem pole".
Describing someone as "___ on the totem pole" is casual but not too casual. It can be used in some formal situations too.