Hi there,
I’m an enthusiastic fan of the Librem 5 and wanted to bring it to your attention, if you haven’t heard about it.
https://puri.sm/shop/librem-5/
It aims to be a phone as open and free as possible, so of course it needs OpenStreetMaps 
As most Linux distros will be installable on the phone, I guess many of the existing OSM clients will work out of the box,
or with little modification. - At least in the docked mode, where the phone acts as a desktop replacement.
I’m just posting this here to spark some interest, and maybe somebody is interested in adapting an OSM client to the small form factor of a 5" touch display.