HI mzanbagi,
PhD programs tend to be really competitive since the number of 'spots' will be small. Since you haven't defined any particular Programs that interest you, your question is a bit vague. Are you asking if there is a School (ANY School), somewhere in the US, that might accept you with a 550 GMAT sco? I'll grant the possibility. However, PhD Programs require a great deal of time, money and effort on your part, so you shouldn't just choose a School that might take you - you should choose a School that really interests YOU for specific reasons.
Here are some things to think about:
1) Is there a particular company that you want to work for or industry that you want to work in? Certain degrees are more appropriate than others if you have a specific career goal.
2) What do you want your MBA to do for you?
3) Do you want to go to School full-time or part-time?
4) Are you willing to relocate? Are you comfortable with working through a program that is primarily online?
5) Are you going to be applying for scholarships?
Etc.
It's okay if you don't have answers to these questions yet, but you should research the options and use those results to plan out the rest of your schedule. You might end up needing to retake the GMAT, but we can talk about that possibility once you've found the School(s) that interest you.
GMAT assassins aren't born, they're made,
Rich