I think that is fine. I know very good Catholics who come early or stay late after Mass to pray the Divine Office on their phones and yes there are a lot of very good apps with prayers and I don’t have a problem with that and maybe that is what everyone was doing. I hope so and as I said as long as someone is being respectful of where they are and who is around them, I don’t think it is a problem.
It is when it becomes texting, giggling and game playing it is a problem and you can usually tell if that is what they are doing. I rarely see something like that happen in our parish.
I guess I do think that if we have to wait a few minutes to answer a text due to safety while driving a car, we should also be able to wait a few minutes until we are out of confession also to answer text messages, so if that would be what they were doing it would be different.