I don't disagree with your thought per se. I'm looking at your train reservation example and think that soon you won't be talking with a real person but two ChatGPTs in a trenchcoat. So corpos aversion to privacy tools drives you to corpo's desire to cut overhead. And I'm sure there are plenty of examples where the phone in option simply does not exist. Or where it cannot exist because they can't find people to staff it or a model to fake it effectively.
I see a future where you sadly have to feed one of these agenetic models, when proven much safer to use than today, with the minimum of information necessary to get your train tickets or whatever, and then let it fight with the other side while you do something else.
I found that's the ultimate decision criterion for me. If you're fine reading on your phone, i.e. you don't lose sleep because of the extra light spectrum you beam into your face, just stick with the phone. It's always there and you are already trained to keep it charged around the clock.
Reading ≠ reading; people have different concepts in their heads. There are people who need the haptics of an actual book. Some may think reading on your phone kind of cheapens the experience. It's where the diarrhea stream of social media also comes through. Or work emails. I've talked with a colleague once and she insisted on a reader device because she didn't want to give the impression she was on Instagram while reading at the airport. So you need to figure out these preferences as well.