Yeah, exactly (and in a more articulate way). Basically, @defmaybe, I would think about it this way: the MFA isn't necessarily a job-market degree even though it's a co-terminal degree--it's really more of an opportunity (in terms of time, space, and community) to develop as a writer. The PhD is going to give you the....opposite of that. Obviously they will try to help you develop as a scholar, but it's less about time and space and more about rigor and preparation. I have a lot of friends doing PhDs--even creative writing PhDs!--who say that they don't have as much writing time as they thought (and some at lit PhDs even say that they have no creative writing time). I think going into that experience before having done your MFA might put a big halt on your development as a creative writer even as I simultaneously believe that lit scholarship is really good for creative writers, simply because of this issue of time--whereas, if you go to Iowa and maybe grow a bit as a writer (and develop routines), you would be more equipped to handle long periods of creative inactivity.
Also, for what it's worth, I do think it is statistically harder to get into Iowa's MFA program than it is to get into a PhD program. And I also think that my MFA years (tho not at Iowa) were so important to my personal development and sense of the world, and I can't imagine a more perfect post-BA experience. So congrats and uhhh...go do that.