I am a MA student and applied for the PhD program at my school. I have a good relationship with several professors but the way their admissions process works, to make it less biased, the professors who know me can't review my application. I got waitlisted and ended up accepting an offer elsewhere. I'm not sure still how your program works though, but I imagine a lot of schools have a similar process.
I agree with the others that getting through the first round of the admissions process will most likely still depend mostly/entirely upon your credentials, unless you happen to get the faculty members you know reviewing your application (even then, it is a committee decision).
However, I do think that if you made it through to an interview, you would then have an advantage! When I interviewed at my undergraduate institution for the PhD program, I definitely felt like a had a home-turf bonus. I was on good terms with many members of the department, which made every interview friendly and positive.
