It seems to me, getting into a PhD program in Economics requires one to first do well in Calc, linear algebra, Statistics, Econometrics, probability and Real Analysis etc as well as score above 160 on the Quant section of the GRE. So focus on doing well on these subjects. Since math classes build on each other you should start taking calculus as soon as possible.
Once you complete most of the above courses with a min A- average you will be able to do well in upper level courses in Economics, participate in some research and earn the type of LORs needed to get into a PhD program.
I think you are making a false distinction between business schools and departments of economics. For example, at Princeton they don’t even have a business school. This doesn’t mean you should stay away from Princeton. At the PhD level, I believe a lot depends on who you do your PhD with (your advisor) and what that professor is known for doing rather than the name of the department or name of a university.
Duke has a highly ranked program in Economics.