As someone with a PhD in a different field who's made that switch, I actually have to disagree with most of the advice here.
This is a bit too bitter and jaded (I'm not quite this pessimistic), but I think it needs to be said to counter a lot of the rosier advice.
Having a PhD in a non-CS field is a _massive_ negative in the eyes of potential employeers. Even if you're looking at moving into a role where your domain knowledge would be immensely relevant (lots of ag + remote sensing startups these days), you will be seen as underqualified compared to someone with only a BS. You'll be seen as underqualified compared to someone with no BS or a BS in an irrelevant field. You need to be strictly better at multiple roles than anyone they could hire to be considered, and even then you'll be expected to work for 1/3 to 1/2 of what they'd pay someone with only a BS and no experience. Folks usually despise domain experts because they see the role of their company as "disrupting" all of the prior knowledge. You represent what they want to replace and you're likely to disagree with them about key approaches.
You will be much more effective, but no one cares about how much you contribute to the company's bottom line. People only care about appearances.
The appearance companies want is a "self taught college dropout". That holds for data science and machine learning positions every bit as much as it does for developer positions, in my experience.
The upshot of this is that you likely know how to learn quickly. Pick up multiple additional skillsets.
You won't get hired because you're an expert in X field that the company needs + a data scientist. You'll get hired because you can throw together a crappy web app on short notice, or debug their crazy duct-tape-and-glue CI system, or save a lot on their AWS bill by switching some things around. You need those skills _on top of_ being a domain expert and a data scientist.
You have to be able to do more than anyone else they could possibly hire for the role to even be considered. Otherwise, you'll never overcome the fact that you have a PhD in their eyes.
Again, that's the bitter/jaded view. Take the above with a grain of salt.