Pat (Winlink) for Librem Phone/Pinephone
Pat is a great program for Linux, Mac or Windows. Unfortunately as of now there is not an official build for Librem Phone/Pinephone.
Once it has been downloaded, run this in the phone's terminal:
sudo cp ~/Downloads/pat-linux-0.12-arm64 /usr/bin/pat
sudo chmod +x /usr/bin/pat
The Pat program requires a callsign and ham radio license to work properly. It can work through a radio or the internet (telnet). Check out the Pat tutorial here.
Pat-Window for Linux with AX.25
The Pat program can access Winlink through radio gateways using a radio, TNC (such as a Mobilinkd), and the instructions as posted here. An easier way to select the serial device and callsign setup can be installed with this Pat-winlink window app: