What exactly do people work on when they are doing a PhD in philosophy?

As Larry said - it's all pretty much the same as in other fields. You have a supervisor or two, and you pick a topic to study that interests you. After a few years study and writing, you have your work evaluated by some external examiners. If it's up to scratch, you get awarded a PhD.Just to add to Larry's points (as he's pretty much covered it), I'll list some of the topics I saw people working on. I don't have their thesis titles handy, but this should be enough to give you a rough idea! What does the Psychology of number tell us about the epistemology of mathematics? What is a just response to global threats such as climate change? What is the correct logic and set theory for Quantum Mechanics? How can it be reconciled with Classical Logic? What is the relationship between information theory in genetics and evolution? Can a multi-valued logic resolve the Sorites paradox? Are immigration laws just? What constitutes a sexual perversion? What did Kant say about X? (there were a lot of these) How ought we to understand the consequences of Gödel's incompleteness theorems. What is unity in science, and is it a virtue of theories? If so, is it a primitive? These are all, in fact, very broad statements of the topics studied. The theses themselves tend to be even more narrowly defined But as you can see, like Larry said, the topics tend to be very specific. Grand, unifying accounts of all philosophy aren't the norm.I've spotted a few other Philosophy PhD's on here, so maybe they can add to the list!And http://www.forbes.com/sites/andygreenberg/2013/08/14/agent-of-intelligence-how-a-deviant-philosopher-built-palantir-a-cia-funded-data-mining-juggernaut/#70e4d8073da8 is the best I could find about Alex Karp. Some kind of social theory. Could be a study of one aspect of social theory ('theory x says y about society, I argue that in fact z') or could be to do with ethics or political philosophy.