I still use an Ubuntu phone (a BQ E4.5) as my daily driver and from time to time an Ubuntu phone tablet (from BQ as well, the M10). I never could connect an external monitor to the BQ E4.5 (AFAIK this is not possible), but the M10 has a HDMI port which works fine. But in this case I use an additional BT keyboard, which has an integrated touchpad too.