Employers don't care what you studied in most cases. I can't imagine any roles where specifically a maths degree would make a difference relative to a maths and philosophy degree. The roles where a specific degree is needed will usually be due to professional accreditation (e.g. engineering roles requiring an accredited engineering degree, healthcare professions etc). Roles which require a more specific background are usually less specific about how that is met, e.g. roles requiring a "numerate" degree would usually accept e.g. maths, CS, engineering, physics, etc, and their various joint honours courses. Unless the maths content was less than half the degree material I doubt there would be any issue.