Replaced? I'm pretty sure for the majority of smartphone users, it is their first computer. You have to be above 25 and and live in a developed nation for you to have had a PC before a smartphone.
In a developing country here. For people below 25, the majority are only familiar with smartphones. I think this comes down to the versatility of these devices(Camera, media consumption, browsing social media, ... ), and sadly that is most, if not all, of their needs in computers ...
I think the format is perfect for consumption. That this is so separated from creation is another problem.