This won’t come as a surprise, but it’s very hard to work efficiently on a smartphone. Even the largest phablets have a screen that’s just too small to contain any significant portion of a document and an on-screen keyboard, and while the apps are there—analogs of the Microsoft Office suite, Google’s collection, and everything in between— actually using them is another matter. The same can be said of tablets; if you really want to get something done on a keyboard-free device, you’re going to have to juggle with Bluetooth peripherals and squint really hard. That said, there’s slightly more screen real estate to work with on bigger devices, and certain examples (the iPad Pro, in particular) are uniquely suited to artistic pursuits in a way that no other device can match.
While the tools on a Chromebook are more limited than those of a full PC, and the power is far less, the laptop-shaped form factor lends itself much more sharply to getting things done. Just about every task can be completed with web-based apps, and (rickety) compatibility with Android apps means you’ll likely be able to fill in any blanks if you run into a wall.