[weberer]

Create a new virtual machine and set the window size to 720x1440 with 2x scaling (or just 360x720) which is what the Pinephone uses. Everything else is the same as desktop Linux, just compiled for ARM.

[selfhoster11]

A touchscreen is probably needed for this. Human fingers are huge and you need to design for that in mind.

[ben-schaaf]

GTK (and presumably KDE as well) supports touch emulation.