Both big Linux Desktops(KDE/GNOME) do try to make the desktop UIs design work on a small screen. Phosh/phoc is mostly GNOME Design and Plasma mobile is KDE.
And that's the point of libhandy(for GTK/GNOME apps) and Kirigami(KDE) to take desktop Applications and make them work on smaller screens. So you can use the same applications on the phone and Linux desktop. And nice bonus is that optimizing the applications to have low CPU usage will have a positive effect on the linux desktop too.
In the case of postmarketOS to give that devices a second life(Hard work cause mainline linux support of most android Phones is bad).
And that's the point of libhandy(for GTK/GNOME apps) and Kirigami(KDE) to take desktop Applications and make them work on smaller screens. So you can use the same applications on the phone and Linux desktop. And nice bonus is that optimizing the applications to have low CPU usage will have a positive effect on the linux desktop too.
In the case of postmarketOS to give that devices a second life(Hard work cause mainline linux support of most android Phones is bad).