将PHP请求路由到App Engine中的子文件夹

To deploy a php app to Google App Engine it says that you need a router, like something in Laravel...the problem is I don't use Laravel (or any other major PHP framework) and I have no intention to. I need to know how to route requests to the appropriate paths in just vanilla PHP. I haven't found any tutorials online that don't deal with a framework or just including client views. Here is what I need:
When a request comes into '/'...it routes to /index.php (obviously this is already happening)

When a request comes into '/account/' it routes to /account/index.php. This is the part I don't know how to do.

I have tried outputting $_SERVER['REQUEST_URI'] and then redirecting the path to the correct place, but $_SERVER['REQUEST_URI'] always just reads '/'.