Hence, the number zero. Philosophy questions everything, even itself. Metaphilosophy is the philosophy of philosophy. Philosophy question everything, even the scientific method, logic, mathematics, etc.
Therefore philosophy is not a part of any branch of science. Not even formal science. Philosophy may use logic, science, reasoning, mathematics, etc., but philosophy questions everything. Of course so does the scientific method.
Metascience? There is the science of science. There is also the philosophy of science. But even if science can question itself, science is bound to a set of rules, whereas philosophy is not. Philosophy can use science, but science must use it’s rules.