Really? This seems a little stringent. High school teachers are busy teaching high school; PhD's are busy conducting research or teaching their own classes. Of course, some of them are going to pick up tutoring on the side for some extra money, but you're screening out huge portions of the available pool of tutors.
Consider my position; I have a BS in Physics and currently tutor a few students--mostly in calculus and geometry. Of course, I don't have "classroom experience," but I've been tutoring students for a while. I know my stuff, and I know when my students don't. I know how to read their math, catch mistakes, and work through their errors with them. I know how to identify recurring mistakes students make and prescribe problems to remedy those errors. I'm not an educator, but I know the subjects I'm teaching. That's as good as any grad student working as a TA, and they're teaching at the university level.
Why the high requirements? I understand the need for quality, but I sense, more often than not, students are looking for someone who knows the material to correct and guide them. You don't need a PhD to do that.