I am a Ph.D. student of Marketing in the University of Texas. Actually, you do not have to earn master degree before you enter Ph.D. program, but they prefer those people with master degree. If you have strong research background and topics, you can convince school. In some cases, schools require students to take master courses before being  Ph.D. students. To sum up, it depends.
The most important is to figure out what you want in the end of the acdamic course. If you want to be a professor in college, PHD is prfered. Also when you finish the PHD it is easier for you to find a job in investing banking as an analyst.