I spent years working on the Ubuntu phone. It was a fully convergent device: by default it would present a phone UI, but plugin an a keyboard and screen and it presents a full desktop UI. The UI was designed by a team of brilliant professional designers and it was a technical success.
Why isn't it around any more?
(1) The carriers. Many people get a free or heavily subsidized phone from their carrier, who makes money from the data charges. Carriers were just not interested in phones from smaller manufacturers, and it's not entirely clear that there is no backflow of cash involved at higher levels. There is also the issue of controlling access to user metadata, always a profitable exercise.
(2) The manufacturers: why would they put a third-party OS on their phone when they control the entire stack from the silicon to the end-user's metadata through their in-house Android fork? They can sell hardware at a negative margin if they can profit from selling access to metadata, or possibly data.
(3) The apps. Developers want to target the biggest, most lucrative markets so they target Android and iPhone which already have a critical mass. You could provide a container to run Android apps on Ubuntu, but then you end up with no differentiating factor except your Android apps look like crap in desktop mode. Running in a container can also restrict the kind of data collection many apps rely on for monetization.
Another problem with apps is that many web services check to see whether the device is iPhone or Android and respond accordingly. Like the browser checks of yore ("you need at least IE 6 to use this site, try updating to a newer browser!") this gives a less satisfactory experience to end users.