I check BMR on mobile only when I'm on my work break, but I'm always on BMR at university. Usually if I feel like I don't really need to pay attention to the lesson at hand, I just start browsing forums or replying to my roleplays.
I do, however, write posts on my phone. Even long ones, and I'm talking posts that are 1000 to 2000 words long. I mainly use my phone when I'm laying in bed and get the urge to write but am too lazy to get my laptop. It doesn't bother me to write a post via mobile, but that's because I text frequently. Normally what happens is that I write an entire rough draft and then read through it again and again, making changes here and there until I'm satisfied. Making an entire post that's around 800 to 1500 words takes me 3 or 4 hours, to perfect and post. It's not that bad for me, but I know plenty of others think differently.
That isn't to say I mostly use my phone for posting. I normally post on my laptop; I only post from my phone if I have a major urge to write, and I already have ideas floating around in my head about what I want to write.