I have gotten many user complaints about this as well. In IOS8 RC/larry was not pretty, but usable. In IOS9 it's not usable on iphone. We unfortunately had to resort to offering classic to people, because the mobile experience of RC with the larry theme is not functional.
I hope there'll be some effort trying to get larry somewhat working again. Dont ask me why, but people seem to want to use roundcube on their mobile phones.
Cor