Rail crimes are one of very few criminal offences in the UK where you don't have to intend to break the law to be convicted.
That means if you can't show your ticket to a guard when requested, even if you did have a ticket on your phone, did have a mobile battery pack, did have a spare wifi hotspot for signal, did have a spare phone incase the first failed, and did have a spare finger in case of your finger suddenly falling off, you are still breaking the law, and can still get a criminal record and go to prison for it.
And due to the way rail companies are allowed to prosecute you directly rather than involving the police or CPS, you can be sure they will prosecute in these cases.
That means if you can't show your ticket to a guard when requested, even if you did have a ticket on your phone, did have a mobile battery pack, did have a spare wifi hotspot for signal, did have a spare phone incase the first failed, and did have a spare finger in case of your finger suddenly falling off, you are still breaking the law, and can still get a criminal record and go to prison for it.
And due to the way rail companies are allowed to prosecute you directly rather than involving the police or CPS, you can be sure they will prosecute in these cases.