Why would you need maths for a philosophy degree? Even a basic pass in maths would be sufficient and you have a good A grade in it at GCSE.
There's logic involved in the course in first year I believe, but this is the kind of basic logic any philosophy degree entails, you don't need to do any more advanced logic options unless you want to.
You can look at all the past papers for the admissions test on the Oxford admissions webpages. I don't see any explicit formal logic problems, although the questions necessarily require you to think logically in a precise way to formulate an argument (but that's realistically an essential skill for any essay based subject too). There usually seems to be one sort of logic-semantics type question in the optional questions section but you could just as well write on one of the others.