It is very easy to install UT.
I have done the same with my Manjora Pinephone.
I downloaded the latest jumpdrive and the UT image.
then i used balenaEtcher to flash 2 SD cards. One with the latest jumpdrive version and one with the UT image for the Pinephone.

You only need the SD card with the UT image to test how the OS runs.
The SD card with jumpdrive is needed to write the UT image to the internal memory with balenaEtcher.

There are really good instructions in the forum.