I "wear off the bike" clothes when touring when I am done for the day so yep, got to bring undies while touring too. They usually act as my pajamas though, especially in the summer so not a total waste of space and weight.
For me running shorts with a built in brief or tights if it is cooler serve that function on tour. So I don't usually carry any underwear.
BTW, another thought on the devices... It is fun (for me at least) to remember that within my adult lifetime there was a time none of these devices even existed unless you count a camera as a device, but even that would be a film camera. No mobile phones, let alone smart phones, no GPS, no laptops, and no tablets, unless they were stone tablets. When you look at it that way, having a smart phone along means having a remarkable amount of capability, that would have been unimaginable not that many years ago, in a tiny device. Folks managed to tour with none of that, so I figure we are pretty lucky to have all that in one little device and I am inclined to embrace that one little device.
Nothing wrong with carrying more if it suits your style, but the phone will really do a pretty good job at a lot of functions that we wouldn't have even been able to do at all (or could do only in a very limited fashion) not that many years ago.