It's very considerate of you to think of it
To answer honestly I mainly use phone in mobile view or full view of site (I don't use app as my phone is low on memory), and I also do write my story on my phone. It's simpler and accomodates my mobility better that way, I can write everywhere everytime I want.
For me, I won't mind to read lengthy paragraph as long as the font size is adequately big (which I think the mobile app is enough)
If you want to specifically ask your reader, perhaps post a status update asking about it.