The Catholic holds that the articles of Faith (i.e. the Creed) are divinely revealed and only received by grace. However, there are certain premises that are known either in themselves or can be known by philosophic investigation. These premises can be known by the pagan. Saint Thomas Aquinas explains:
The existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature, and perfection supposes something that can be perfected. Nevertheless, there is nothing to prevent a man, who cannot grasp a proof, accepting, as a matter of faith, something which in itself is capable of being scientifically known and demonstrated.Saint Thomas Aquinas calls our natural knowledge of things the "preambles of faith" or the "presuppositions of faith" (cf. III Sent. d. 24, a. 3, sol. 1). The preambles or presuppositions of faith include the premises that God exists, that God is one, incorporeal, and intelligent. None of these facts pertain to the Gospel and they are not articles of the Faith per se (i.e. the dogmas of Scripture and the Creed). Note well that knowledge of these facts does not necessarily entail salvation. Salvation is attained by calling upon the name of Christ and in believing the entire Christian Faith. However, the Christian Faith also assumes all of the preambles of the Faith because the Creed assumes that God exists, that God is one, etc.
Summa theologiae Ia, q. 2, a. 2, ad 1.
Consequently, the Catholic does not hold that mere philosophic knowledge is sufficient for salvation. Philosophy merely establishes the bare-bones presuppositions of the believer's saving faith in the Gospel. Catholics also recognize that most people do not come to believe in a Creator because they happened across the cosmological argument for the existence of God. Your pew lady already assumes everything the greatest philosophers achieved by virtue of her believing the tenets of the Christian Faith.
This leads us to an obvious question: If faith supplies all the basic concepts that reason can attain through philosophy, then what is the use of philosophy?
I believe that many Protestants (and even some Catholics) are afraid of philosophy because it seems to assume that faith is unnecessary or that there is "another track" to heaven through speculation. Rightly understood, however, philosophy does not compete with theology but confirms it. This brings us back to the purpose and role of philosophy. Since grace never destroys or contradicts nature, so also faith never contradicts reason. This truth assumes that the Christian Faith will always be whole and coherent.
The Christian does not fear reason, but he embraces it. As my professor Fr. James Lehrberger O. Cist. is fond of saying, faith does not fear the "acid bath of reason" because we know that faith will always emerged unscathed. Reason is not able to grasp naturally the divine truths of our Faith (e.g. the Trinity or hypostatic union of Christ's nature), but once we come to hold these truths by faith, we discover that reason certainly does not contradict these truths. As St Anselm said: Credo ut intelligam. "I believe so that I may understand."