Philosophy and literature are artifacts of human culture--that is, they can only be understood in the context of human culture and society. In contrast, scientific facts like the mass of the proton are exactly the same everywhere in the universe (or so we presume).
That doesn't mean that philosophy and literature--and art, and music, and film, and all the other "humanities"--aren't part of human knowledge. They are, and they can have profound impacts on human society, which in turn, has significant impacts on the physical world on the Earth's surface.
When humans interact with the physical environment, we use heuristics to model the physical realities of nature in a usable way. Think of catching a baseball; we have an internal model of the Earth's gravitational field that allows us to predict the path of the ball, and place our hand in just the right spot to catch it.
When we interact with other humans we use heuristics too. These are affected by the cultural experiences we have, which include art, stories, movies, etc. When we evaluate a politician, for example, we are applying the heuristics developed by hearing, seeing, and telling stories. We think one guy looks creepy, and another trustworthy...why? Because of what we've learned about humans so far, and a lot of that comes from literature, art, philosophy, etc.
I have a PhD in Classics. My focus was on ancient philosophy, in particular on Epicurean philosophy, in particular on a Roman Epicurean named Lucretius, in particular on Book 3 of his De Rerum Natura, in particular about his arguments against the fear of death in that book, in particular about the structure, formal & logical analysis and evaluation of his argument for the thesis that "death is nothing to us" in the later portion of Book 3. (De Rerum Natura is a Roman philosophical poem from the mid-first century BCE. Lucretius and his poem are getting a lot of press recently because of a book called The Swerve by Stephen Greenblatt.)
The linked guide to PhDs made me smile, and it rings true to me for non-sciences. As an undergraduate I was a Comparative Literature major with lots of credits in Latin, Greek and Philosophy. Once I got to graduate school for Classics, my studies became increasingly concentrated in smaller and smaller areas of an already small field (Greco-Roman antiquity).
tl;dr I think literature and philosophy PhDs are also pimples of knowledge.
As for whether or not we expand human knowledge, that depends on how you define "human knowledge" and "expand", I suppose. I think it's charitable to say that (many? some?) people produce PhDs that expand human knowledge of Homer and Dante and James Joyce and Plato and Nietzsche and so on and so on. But of course if your definition of "knowledge" only makes room for numerical or quantifiable or experimental subjects, then you may disagree. I arguably expanded the world's knowledge of De Rerum Natura. My work has been cited at least once that I know of in subsequent work on the Epicureans, and not by me. (That's not just a joke: I remember reading that a large percentage of all research across disciplines is only ever cited again by the original author. I find that depressing.) I've also met a handful of people who tell me that it helped them in some other study.
I don't know much about literature, but I know philosophy is very important to the sciences. Especially the philosophy of science. Philosophy also deals with important things like logic, inference, etc. I took a couple philosophy courses, and was surprised how rigorous and technical they were.
