5th Year PhD student here. On the flip side of Jellyfish's comments:
Fields vary, but in general, a PhD is not for the faint of heart. They are long, poorly paid, and ego-annihilating. They are not about learning, although that happens incidentally, they are about creating new knowledge, most of which nobody else will ever care about. It's an all-or-nothing deal: leave part-way through and you get nothing. They're also not really about intelligence. While you've got you to be somewhat above-average intelligence to make it through, getting a PhD is mostly about persistence. Maybe organization psych is particularly fast, but 4 years is uncommonly quick to finish, too. I'm graduating at the end of this academic year, and will be tied for fastest to ever graduate from my program.
They're really only worth doing because there's a specific (or several specific) jobs you can point to that you must have a PhD to do. The standard example, of course, is "Professor". Note that competition for Academic jobs is an absolute bloodbath, and the usual result of doing a good job after getting a tenure track job is to be denied tenure - i.e. fired.
That's not to say don't do it, while there are a number of things I would change about my going to graduate school, I would probably still do it again. But it's not a simple decision, and it's best to have very specific reasons in mind for getting to the end, because otherwise you'll get three years in, and wonder why the hell you're putting yourself through it all.