That statement was from Chiltern, I've not seen it on any others.
If you know anything about the demographics of most of Chiltern's area, you'll know that the number of people not owning smartphones (likely premium ones at that) will be very close to zero. And they have some spectacularly pointless booking offices, such as Aylesbury Vale Parkway (highly questionable why any sort of building was provided at that station given how recent it is).
Bit in bold - because as I pointed out when you peddled this yesterday, Aylesbury Vale Parkway station opened in December 2008 - that was only a year after the first iPhone was launched. The station would have been planned 4-5 years before then, when nobody had a smart phone and nobody knew what shape they would take.
It's easy to throw stones, but the decision to put a ticket office at that station, particularly given the number of likely season ticket purchases, was sound *at the time the decisions were being made*. Had it been built 10 years later, different decisions could and probably would have been made.