It varies by school. Some schools use their master's program(s) as feeder programs into their PhD programs (The New School...if I am remebering correctly, some counseling programs also do this. Pepperdine does this for their Psy.D. program). Some programs have classes where both masters and doctoral level students take classes, those programs probably would be more open to matriculation....but you'd have to apply just like everyone else and make it through the front door. Other schools have completely distinct programs that don't have any crossover. One line of distinction tends to be if the degree is terminating (meant for licensure at the MA/MS level once completed). Typically if you are in a terminating MA/MS program, it is the rare exception and not the rule that you would go on to a Ph.D. program.
Most applicants for doctoral programs do not complete an MA/MS first (<20%). Some counseling programs are the exception, as they traditionally have a higher % of students who get an MA/MS first. A few programs actually require an MA/MS before you can apply, but they are in the minority.
I would be wary of any university that encourages students who don't get into their Ph.D. program to do a terminating MA/MS program instead. The reasoning is that many universities use their MA/MS programs to offset the cost of their doctoral programs. One of the dirty little secrets of graduate training is that most MA/MS/similar programs are cash cows. The doctoral programs produce recognition and increase status, but they typically hurt the bottom line. Research $'s cover much of the cost for faculty and a % of the doctoral student's cost, but facilities and other hard costs need to be paid for by other means. Increasing enrollment in unfunded programs helps offset these costs.
There are also MA/MS programs that are setup specifically to prepare students for Ph.D. programs. These programs tend to be highly selective, are sometimes (partially) funded, and typically focus on stats/research/experimental training. You won't do therapy, you won't be license elligible, but you will be a more competitive doctoral applicant. Wake Forest offers one such program, and I've heard from multiple places that their students are very competitive for Ph.D. programs. Avoid any program that offers "specialization", unless you thoroughly vet the program and check with academics and professionals outside of their system. Most "specialization" programs are more marketing than substance.
OP, I'd let your mentor know your goal of getting into a doctoral program. You also want to ask if previous students have enrolled in the MS program, and then later moved on to doctoral training. You'll want to know if they stayed within the university, or if they went to another university. You'll also want to know if the doctoral program has an official or unofficial policy about "home grown" applicants. Lastly, you'll want to ask your mentor for an honest assessment of your viability as a doctoral candidate. You need to know where you are weak, and you need to address those weaknesses either by doing work with your mentor, or seeking additional training/experience outside of your program.
ps. I guess I was right about The New School...glad I'm still up to date with this stuff. 😀
