You need to target schools outside the top 16, maybe even outside the top 30.
With the current GMAT that you have, you will be a stretch for USC, and maybe even UC Irvine. You need to adjust your expectations as you're competing against a lot of candidates who simply have stronger credentials than you do.
In any case, if you're interested in doing a PhD, you really need to boost that GMAT score as PhD programs put an even greater premium on strong scores than MBA programs do. As far as I know, most reputable PhD programs (and if you're going to do a PhD program, it is extremely important to go to a strong program if you want to stay gainfully employed in academia) want to see at least a 700 or greater on the GMAT.
Do whatever it takes to boost that score. Or frankly, you'll have a hard time getting into a decent program.