Personally I don't think a phone could completely replace a desktop/laptop for me. I can't imagine any sort of media creation (text processing, programming, photo editing, etc) on any phone would be better than that of a traditional computer. The UI just isn't equipped for it. I feel this was something that Microsoft overlooked when developing Windows 8 for a tablet-only environment. Phones can easily replace computers for people who just want to consume media, but they're completely ill-equipped for people who create media.