I'm actually not sure about the "one big touchscreen" idea - it's seems likely some designer considered it, but even Star Trek TNG PADDs had more than one touch display segment.

Portable radio-type devices have been all over, portable computers as well, and networking radios autonomously together made appearances. Ditto for adding a camera to standard communications devices. I'm not really sure how much of it you need going at once to consider it a smartphone.

Like the guy in the link mentions, what people would choose to do with them and just how often was the hard thing to predict. When someone pops open a version of the internet in Heinlein it's always to do research. It's never cat pictures or porn or to post a random picture of themselves and what they're doing. Usually the computer is part of your spaceship or whatever, not in your pocket, just for that reason.

The Star Trek Communicator somewhat resembles it, and that is from 1964.

The first commercial smartphone was released 31 years ago.

https://en.wikipedia.org/wiki/IBM_Simon