Right now FCC isn’t optimized well for mobile use, but I believe that is because mobile support is one of the UI improvements that will roll out incrementally. That won’t solve your keyboard issue though, which I would also find very frustrating. It sounds like you do have a computer but that you only connect to the internet via your phone. Is your computer a laptop that you could take to an internet cafe or library occasionally? If so, you could set it up for offline development in a few different ways. If you have the ability to transfer files between your computer and your phone, you can experiment with saving solutions as files and pasting their contents into FCC on your phone.
If you come up with a good solution, please come back and share it, because you’re not the first camper to ask this question.