@SteamLouis-- That may depend on the school and the course. In my school, economics courses were only taught by professors. PhD students usually worked with professors as teaching assistants and there were also times when they filled in for the professor if the professor couldn't attend a lecture for some reason. Some schools may allow their PhD students to teach basic courses like economics 101. All economics professors have teaching assistants to help them with their lectures, course materials, grading exams, etc. So even if PhD students can't teach, they can work with professors.
At my school economics PhD students also worked in what we called "economics workshops." They basically helped economics students with their homework and economics theories from class. I used to go there when I didn't understand a subject.