I would still like to know just where this "QR code on your phone" is. My email from 12306 confirming ticket purchase does not have one. Neither can I find one on the 12306 app. Perhaps you can post an image?
When you buy on 12306 (on the website - no idea about the phone app), there is the option to generate QR code. Another friend was able to take his train using the QR code, the staff seems to get more familiar with this.
Some ticket agents (at least china-diy-travel) will send you the QR code if you wish. For now they still generate the Exxxxxxx code to pick up tickets if you wish.
This is only around Shanghai now but will be everywhere eventually (not sure about year-end as previously announced). I have seen the new equipment in train stations in Yunnan.