I can tell you that I am currently a first-year in an English/Creative Writing PhD and my university will only take 9 credit hours of coursework from an MFA. Some programs take more, but if you are going for a studio MFA and then thinking about a traditional literature PhD be prepared--they may only take a few of your classes. Even if you want to stay at the university where you got your MFA and do your PhD there, they may not be able to take many of your classes. I'd say look at the schools you are thinking of; often they will state how many credits they will transfer in from an MA/MFA. Part of it comes down to the guidelines--as an MA student in English, you are fulfilling course requirements (early British, late American, etc.) Most MFA programs don't put any restrictions of what literature classes you take, as long as they are at the graduate level.