TLDR, install Manjaro Posh.
The developer who worked on Lomiri hasn’t returned yet as he was/is sick. See here. Lomiri looks good, the UI is great and looks very polished but it’s in unfinished state. Great if you want to give it a try just be weary that there will be a lot of items that don’t work yet (for example, the notification toggles).
If I recall correctly, the plan was to launch Manjaro CE with Lomiri but the situation changed with the lead dev of that spin being unable to work on it.
Plasma Mobile is work in progress. Personally, I find that it likes to hang a bit (everything going greyscale) but still worth a look.
Posh so far is ahead compared to the other 2 options. Posh itself has received the most attention from various projects that directly reflects on Manjaro’s spin. The desktop mode is rather interesting (requires kb/mouse) and overall works well. Different than most mobile experiences you would be used to from Android world yet refreshing and fitting Linux well.
If you like to experiment or just want to check what your options are, I would recommend you to put megi’s multi-boot image on a sd card.