I don't think cash can be phased out. Coz the elderly need them and cash is the most stable money in the real world. What if electricity breaks down?
From my little understanding, seems they want to phase out physical currency to be able to properly monitor how people use their money, to be able to have more control over the financial system, for the sake of hygiene etc...
Well, I don't believe they can phase out physical currency if they really understand what currency is.
I guess they could impose this in places where people/things are sufficiently controlled by them or an entity.