I always roll my eyes at writers that advertise themselves as having a PhD. I certainly wouldn't hire them and I think they are being very misleading.
You see, not all majors have a PhD as their terminal degree and writing is one of them. If you want to be a creative writer, you get your Master's degree. What this means is that people who advertise themselves as writers with a PhD, either do not know what they are talking about or have a PhD in something else - such as business or biology - and then let people assume that their PhD is in writing.
You may be thinking - but if I am writing a fiction book like Jurassic Park, wouldn't I want a biologist or paleontologist with a PhD helping me? Uh... no. I have a B.S. in biology - for that degree, I needed to take all of two writing courses at a whopping 6 credit hours. I have read a lot of biology journals - let me tell you, it shows in their writing. I have also taken numerous biology exams where I wished the teacher had taken at least enough writing courses to create coherent questions.
After a biologist gets a Bachelor's Degree, they never have to take another writing course again. They will be doing a lot of writing on their thesis and dissertation, but they can hire someone like me for content editing to help them. In fact, there are many teachers who recommend their graduate students do this because they do not have basic coherent writing skills.
For the record, I have taken more than the required writing courses. I took creative writing, two fiction writing courses and two literary/play analysis courses. But that is why I have two undergraduate degrees with 256 credit hours and no masters degree (sigh). At this point in my life, I would like to get a Master's degree in creative writing, but I have to pay off my college loans first - 256 credit hours is expensive to say the least.