I don't know what phone you have, but I wouldn't know where to begin to learn programming on my phone. But I started learning programming at 6 years old on a desktop computer.
As did I - on an 8088 that I still have around! But you know, I was drawn to things like that. I read every page of the several hundred thick binder that came with it, and tinkered with everything it described - even the things that weren't really much use. I lamented the lack of a hard drive, so I could try out the drive initialization and head parking commands (why? Who knows! They were there!). MS-Debug was a gold mine where I could play around with this arcane Assembly language. I couldn't build anything significant, and I tended to crash my system a lot, but it sure was fun! I tinkered with everything, really --- mostly electronics, but some mechanical devices as well.
But you know, how many kids are like that? Given that and a tablet... most kids would just take the tablet. I think the ones who are like that, will find their way to it anyway, given half a chance (so exposure is still important).
Maybe there's some sort of middle ground - mobile games/apps that employ the same basic concepts as programming, to act as a gateway?
Or maybe in a decade we'll just have holographic haptic keyboards that are trivially portable...
