Last time I did that, the phone wiped the magnetism off the ticket. I took my phone out of my pocket and it had the ticket caught on the casing, so things didn't look good. Sure enough, when I got to Liverpool Street the barrier wouldn't accept my ticket; I had to show it to one of the people on the gate. I tried to use it to get to the platform for the train, but again it didn't work and I had to show it to the person on the gate. Finally, when I got to Colchester, it failed again; again, I showed it to the person on the gate.
At that point I decided I'd throw it away in the station bin. I also had the receipt I got when I bought the ticket to throw away. Except, hold on, where was my receipt? It was supposed to be in my left pocket where I kept the phone, but it wasn't there. I had my ticket in my right pocket, to keep it away from the phone, so I checked my inside pocket and found ... my ticket. I checked the ticket I'd just shown the inspector, from my right pocket, and it was the receipt.
I guess what happened was that when I took my phone out of my side pocket, it brought the receipt with it. It stayed stuck to the back of it while I did the text message, then I put both of them in my inside pocket. When I removed it and spotted the receipt, I thought it was my ticket. After all, who pays attention to what a ticket looks like?
Certainly, three ticket inspectors whose job it is to check tickets don't.