The FuriPhone FLX1 meets all of your requirements:

• It runs the Debian-based FuriOS, which is FOSS.
• Among phones with Linux (excluding Android) preloaded, its specifications are among the best available, including a camera with PDAF and OIS, a 120Hz screen, and a replaceable 5,000 mAh battery. It also supports 5G and VoLTE, and has IP68 water resistance.
• FuriOS includes Android app support via a fork of Waydroid.
• The phone and the Linux distro are actively maintained.
• Furi Labs is based in Hong Kong.

Also, make an account on OpenStreetMap (OSM), which is what Organic Maps uses for data. OSM is the Wikipedia of maps. You can use Organic Maps or any other OSM editor to add anything that’s missing and correct anything that’s wrong or out of date, then see your changes in the next map update.