You'll certainly be able to install it on your phone, but Ubuntu can't reasonably count on that only to get adoption. If manufacturers don't ship Ubuntu phones, the OS is doomed.
Well to quote Torvalds himself, "most people don't want to install an operating system on their computer of cellphone".
This is probably the #1 reason for lack of uptake of Linux on the desktop.
The problem is extra hard with phones because manufacturers seem to have more measures in place to prevent people from easily installing third party operating systems.
