I have MD PhD and I can tell you PD's like to see the FMG's have them. There are many PD that will not interview you if you are a FMG w/o a Phd as well.
If you are US grad, I am not sure. I can tell you it is not a bad thing. Some may say that more letters mean you are more research. I will tell you it is not true. It depends on you focus of the Phd.