It's not that it's impossible, but it's not trivial either. But mainly, it's just unnecessary.
If the user is not fooled by a well crafted phishing, by doing the most trivial countermeasures such as calling back, they are not going to be fooled by a deepfake. In practice work on phishing is mostly better spent elsewhere. So while we shouldn't dismiss it completely, it's clearly not the case with a smallish company with limited economic value, so very unlikely the case here.
There has been a handful of highly profile media cases involving deepfake. None of which has held up on further investigation. It is understandable, nobody wants to be known as the one who didn't recognize his own kid on the phone, but the truth is more simple and actually helps us when designing countermeasures.