Zsolt Benke writes that "a compelling use case for a big iPhone and a small iPad mini is using them as a mobile writing environment" where most people consider them content consumption devices.
I couldn't agree more.
I have said for at least a decade now that my phone is my PC – that's primary computer – and almost everything I do happens there. Reading, writing, image editing, even coding.
I moved from the iPhone 4S (which was already central to my online life) to the Nexus 5 in December 2013 due to its larger screen and never looked back. 2014 saw me type around 110,000 words for the #write365 project alone. All on the phone. All using the on screen keyboard.
With screen sizes increasing, and the convenience of always having the it to hand, it became second nature to use the phone as my main writing environment. In fact, I usually have to force myself (as I am doing now) to write on the MacBook due to it not always being readily available and requiring a degree of preparation.
As Zsolt says, tapping away on a phone may seem "an ineffective way to write" but, just as the best camera is the one you have with you, the best writing environment is the one available and we quickly adapt to its limitations.