Easy to go from MA to PHD program?

Hello, I am an undergraduate student looking forward to graduate study for IO Psych. I was wondering: (1) Is it easy/ normal to switch from MA to PHD program while in graduate school? (or vis-versa) (2) Is it easy/ helpful to practice with an MA, then pursue a PHD after a few years of practice? If possible, how long would it take me to get a PHD after I've practiced with my MA a few years?

Thanks!