Yes, Canonical (the company behind Ubuntu) is no longer developing for phones and tablets. In addition, in Ubuntu 18.04 LTS, the default desktop shell will switch from Unity 7 to GNOME Shell. Development on Unity 8, Mir and phone/desktop convergence will come to an end. Existing phone and desktop releases will be supported for their normal lifecycle.
This was officially announced in a post from Mark Shuttleworth, founder of Ubuntu and Canonical, on the Ubuntu website: https://insights.ubuntu.com/2017/04/05/growing-ubuntu-for-cloud-and-iot-rather-than-phone-and-convergence/
Since these are free software projects, someone else can take over development and maintenance. Right now (April 2017) these communities are looking into it:
- UBports, porting what used to be "Ubuntu Touch" to multiple mobile devices
- yunit, continuing development of Unity 8, with a desktop focus
- and there is possible collaboration between the two
...at this stage the discussion is mostly technical and it is yet to be seen if these communities have enough resources for long-term development.