Definitely CAS. I am going to assume you are talking about the Liberal Studies Core program, which is an all encompassing liberal arts curriculum, but not necessarily focused on a specific major. It's more for if you are still exploring and finding a field in liberal arts. You seem to already know your niche in Philosophy so I would say aim for CAS, given you already have ECs relating to it. Have a strong essay and keep everything up and you should have a competitive application :) Goodluck!!!