Imagine receiving a deepfake video with audio from your boss telling you to do something.
Do you really think that most employees would need more than that?
But yes, at my current employer, I believe no one would do that just based on an email and a phone call. But then I dare say that faking Swiss German is an order of magnitude harder than faking English.
Someone has compared the typical cadence of Schwyzerdütsch to riding a donkey over very rough mountainous terrain, and I'm inclined to agree.