Ye ol' blockchain
I expect that the digital Chinese currency will have built in tracking. The government will know who has what and where it's been. Physical cash can be nice and anonymous, but digital money is surveillance squared. Everybody will be instantly trackable everywhere they go. If you don't have a phone, you won't be able to have money. Even little kids will need phones or their grandparents can't give them money for ice cream, candy and all of the things the parents would rather they didn't have. Every small trader will be tracked and taxes helpfully deducted by automatic payment.