Hi stephjayg,
You have a number of different questions/issues here, so I'm going to break this down sequentially.
Most Test Takers need 3 months (or more) of consistent study time to hit their respective "peak" scores, so I'm not surprised that your second Official GMAT score wasn't a 650+. Considering that you probably took your second GMAT a month after your first one, the fact that you raised your score 90 points is commendable.
Can you post your Quant and Verbal Scaled Scores for these two Tests?
Taking LOTS of practice CATs was/is NOT the solution to your problem. A practice CAT is just a "measuring device" - taking lots of CATs is the equivalent of frequently standing on a scale and being disappointed that your weight doesn't change. Learning, practicing and mastering content and tactics is how you improve. Putting in the necessary time and reps to learn more than one way to answer questions and remove any/all silly mistakes from your work is how you hone your skills and score at a much higher level.
Can you post your Overall, Quant and Verbal Scaled Scores for each of your practice CATs?
A 620 is actually pretty close to a 650, but my guess is that you approach this Test in an inconsistent way and you're making too many little mistakes on "gettable" questions. You mention taking the GMAT again in January, but when EXACTLY is your Test Date? And when are you planning to apply to Business School? Would you be able to push your Test Day back if you needed additional study time?
You mention applying to a PhD program, but you haven't offered much in the way of details. PhD programs have a much smaller number of applicants than MBA programs, but also only accept a small number of total students. As such, applicants have to be specific with their desires and applications tend to be really scrutinized. Here, saying that you're interested in a PhD in either business strategy or marketing is such a vague answer that a PhD program probably would not accept you for that lack of specificity (the other applicants would likely be able to describe, in detail, why they wanted the degree, what they would use it for, why it has to be from that specific school and why it has to be right now).
This is all meant to say that while the PhD "part" of your plan is clearly several years away, it will require a significant amount of work on your part to craft THAT application. When you get to that point in the process, you might consider working with an Admissions Expert. You might even have to retake the GMAT again (if more than 5 years has passed, then you'll absolutely have to).
For right now, there are some things that you can do to improve:
1) Focus on defining your mistakes and fixing them. This does NOT mean that you should take lots of additional CATs. Since those scores are all lower than your goal, then your "mechanics" are the real problem right now. Don't try to fix every single problem, but fix that ones that the silliest and easiest to fix.
2) Define your overall plan with specific dates and contingencies.
3) If you're running into trouble with your work, you should post questions in the Quant and Verbal Forums. You'll learn a lot from the experts and other users.
GMAT assassins aren't born, they're made,
Rich
I retook it with some studying a couple weeks later and got a 570. I am highly dissatisfied with my score so I've been studying diligently since and have been taking MANY practice exams. The highest score I got on my practice exams was 620. I have followed the 60 day study guide plan provided by beatthegmat.com and signed up with Magoosh. I do have test taking anxiety though. I just get so nervous! I am retaking the GMAT in January 2015. 
