Taking standardized tests is part of the process to apply to Business PhD programs. In order to show your academic prowess compared to other applicants, you can take the GMAT or the GRE. Many schools accept either the GMAT or the GRE, some prefer one over the other, and some accept only one of them.
This time I will write about the GMAT. There is really a lot to know about the GMAT, one could do a whole blog just about the GMAT. But, in short, the GMAT is a test to evaluate your quantitative and verbal skills. It is very important in the PhD application, since your GMAT score is one of the first things admissions committee look at when evaluating your profile. A low score may show them that you are probably a waste of their time, while a high score may show them they should take a better look at you.
It is also very important because you will probably need to devote a lot of time preparing for the GMAT, even if you are academically very strong. People say that the GMAT tests how good you are at taking the GMAT. So, you may be great at math and still do poorly in the quantitative section of the GMAT if you don't know how to face the test. At surface, the GMAT tests mostly your mathematical and English language skills. But it is much more than that. It tests your ability to make decisions, to identify your strengths and weaknesses, to manage your time, to deal with pressure, to build up your mental resilience. Lots of applicants are great in Math, but get low scores due to bad time management or panic attacks during the test, for example.
For me, preparation for the GMAT took about 1 year, since I had to revise mathematics which I had not studied for more than two decades. And one of obstacles I had to overcome was to learn to give up on a question which I knew how to solve, but not in the short time demanded by the GMAT.
The whole test will take about 4 hours, And you gotta be able to keep your mind sharp during the whole 4 hours. If you lose focus midway, you may doom your score. A mistake people make is studying for the GMAT only in short bursts, like 1 hour a day. You should include long sessions in your preparation, because you gotta be able to solve extremely hard questions after several hours of mental work.
The most important sections of the GMAT are the Quantitative and Verbal Sections, each with scores ranging between 6 and 51. The scores of both sections will be combined in some strange way, resulting in a "total" score between 200 and 800. For Business PhD programs, your quantitative skill is usually very important. Specially in for programs like PhD in Finance and Accounting, your quantitative should be close to a perfect. But even for other fields, like Marketing, your quantitative score should be very close to perfection. Scores for the verbal section are lower, it's almost impossible to get a perfect score of 51 in verbal.
The quantitative section has 41 questions to be solved in 75 minutes. The verbal section has 37 questions to be solved also in 75 minutes. Both sections are CAT (Computer Adaptive Tests). That means that if you get a question right, the computer will adjust the test to give you a harder question. And if you get a question wrong, the computer will give an easier questions. It is not that simple, but it's something along those lines.
If you are planning to apply to PhD, you are aiming a great score. So, you should expect to get a medium question first, then a more difficult, then another even more difficult, and so on. If you keep doing good, by the 20th question in a section you will start to see very hard questions. To get a great score, you must expect to face increasingly harder questions which will test your limits, even if you are a genius.
I found the verbal section easier to deal with, even being a non-native. The verbal section has reading comprehension, critical reasoning, and sentence correction questions. So, no great surprises in there. You probably saw those kind of questions before. It does not mean they are easy (reading questions include very complex and boring texts to be analyzed, for example), but they are typical questions.
The quantitative section, on the other hand, tests knowledge you possess in unexpected ways. You may get angry with yourself when you get wrong a question about something you thought you mastered. Special attention must be given to a kind of question called Data Sufficiency, where you must answer if the question has enough information to be solved. So, you're not being asked to really solve the question, only if the question can be solved or not. You must often hold back that urge to really solve the question, because doing that will take precious time. As far as I know, GMAT is the only test which uses Data Sufficiency questions. I had to take a time specifically to learn how to deal with those questions effectively.
There will also be an integrated reasoning section and a writing section, whose scores will not count towards that "total" score I mentioned above. Even if they are considered by many as less importantt than the quantitative, verbal, and total scores, you must not negllect them. Bad scores will taint an otherwise great application.
You get the scores, but also percentiles for each score. So, schools what your score means, when compared to other people who took the test. My total score was 750 / 98% for example. That means that my score of 750 was better than 98% of the people who took the test recently.