Philosophy is generally predicated on, and perhaps more about, asking questions rather than finding answers. It's a search for wisdom, not truth. The only thing that all philosophers would all agree exists, besides themselves perhaps, would be questions. And sometimes, philosophers will pretend that even those don't exist. So, philosophy doesn't, as a whole, assume that any axioms, or fundamental rules, exist, upon which to build "true" or "false" answers.
Proof is a concept in mathematics, and mathematics is in some ways a formalized version of philosophy that HAS acknowledged the existence of fundamental rules (axioms). It is also a concept in legal systems, where again, you have formal systems that have fundamental rules (laws).