You need to decide what your end goal is. If you want to practice medicine in the US, pathology would be a field where you would actually stand a chance to match, as ~50% of IMG applicants even with a score <200 managed to match over the last 5 years:
Tableau Public . No guarantees, especially since that chart doesn't take into account that this was your second attempt. Realistically, none of this matters until you get a step 2 score--realistically you have no room for further mistakes, and if you get a fail on either CK or CS then you probably need to accept that you're not going to get a US residency.
Getting a PhD actually seems to REDUCE your odds of matching--to 40% in pathology, and in FM your odds go from 25% to 11%. Perhaps a subset of the applicants with a PhD pursued that degree as a perceived way to overcome an especially weak application, for example multiple board score failures or minimal USCE. In any event, none of the residency programs that you could potentially match at are going to be research powerhouses, so the PhD is of little use to them.
So my advice is that if you believe you're not going to be able to match and you're looking for another way to come and train in a science-oriented field in the US by pursuing a PhD, then GRE might be a reasonable option. But I would not go that route thinking that you would be improving your standing for a future residency application. The data does not support that going that route would help.
