For All X, There's Philosophy of X...
... one only needs to plunge to the foundation. The issues at the foundation are always the same: What there really is, how we know about it, what separates the good from the bad.
If one delves deeply enough, with sufficient generality and abstraction, the foundational issues about X will reveal their kinship with foundational issues in other areas. Discussion of them can thus be illuminated by knowledge of how similar issues are treated in other areas -- the philosopher's special expertise.
Consider the philosophy of hair, for example. At the foundation: What is a haircut, really? How much does it depend on the intent of the hairdresser? What makes a haircut good or bad? For example, must it please its bearer? Is it relative to fashion, and if so how locally? How, if at all, can we settle disputes about the quality of a haircut? A true philosopher of hair will have informed opinions about such matters. The answers to these questions might differ from the answers to similar questions about, say, painting as an art or about the morality of charitable giving, but a family resemblance should be evident, along with the possibility of cross-fertilization.
Consider also: The philosophy of Coke cans, the philosophy of starlight, the philosophy of football, the philosophy of birds, the philosophy of siblinghood.
To the person with the right turn of mind, perhaps, all thought becomes philosophy.