You can RP all you want on mobile devices. I think he meant that it's best not to post big intro threads on mobile
Yup. This.
Writing a typical post from mobile isn't a big deal (especially if we're just talking about OOC posting). But, when you're going to post something where presentation matters (like the first post of an OOC, interest check, or that sort of thing), then I would definitely wait to get onto a computer.
If computer time is scarce for you, then I would recommend drafting important posts out on paper first to better organize your thoughts. That way, you don't have to spend so much of your computer time thinking your way through writing it. Most of the work from then on will just be typing it up, proofreading, and formatting.
Also, since you
did start this thread asking about how to get players and not just about how to improve your formatting, I definitely suggest posting up an interest check or RP ad (or both) so that people actively looking for new RP's to join can more easily find yours. Also, the seeking group invites forum is pretty great, too, as you can quickly hand out invites to a bunch of people.
For more detailed advice on aggressive advertising, you can check out the post I made
here. Although it was directed at someone else, I think most of what I said here would apply to anyone looking for more players. Unlike the OP of the linked thread, though, you don't exactly have a super niche RP that would be really hard to advertise for, so, you don't have to go quite as balls-to-the-walls as I suggested doing here. XD I imagine that just following at least
some of the suggestions here would get you a fairly respectable number of players.