Honestly math courses you have already taken are more than enough for admission to PhD in econ, master's in math will not have that much marginal contribution to your profile. You should take more graduate level economics courses and see whether you really want to do PhD in economics. In your senior year you may also try to catch a pre-doctoral RA position at some credible institution, that will be considerably better for your admission prospects than a further master's in math. Given that you are already at a top-10 US college, chances that you'll get admitted to top10 are already higher, but you should be confident that economics is what you want to do![]()