Never used any kind of ticket on a phone simply because I might lose the charge and get "gripped" or even forget my phone altogether (I don't use it constantly), whereas my wallet with a paper ticket in is always in my pocket.
However I was watching "Countdown" of all things where a contestant who is a train conductor told us that he always carries a pair of chargers for those whose phones need recharging on the journey. I found this a stunning piece of thoughtfulness and initiative, unless of course his employer takes a dim view of this and would much rather he charges the passenger rather than the phone!