There was an effort to support Ubuntu Touch, as announced by Purism. Some work was done, as evidenced by commits and images - don’t bother trying these, they did not really work on my Librem 5 Evergreen.
Generally, as seen with the PinePhone port, running Ubuntu Touch on a mainline device, introduces some issues not seen on Android devices with hybris/halium. If you want to port Ubuntu Touch to the LIbrem 5, the recent community port to PinePhone (Pro) may help.