To conveniently copy files to your Phoniebox via network samba can be configured during the installation. The folder ./shared/ will be exposed as network share phoniebox, giving you access to the audio and config folders.
To access the share open your OS network environment and select your Phoniebox device.
Alternatively directly access it via url with the file explorer (e.g. Windows \\<ip-address-of-your-phoniebox>, MacOS smb://<ip-address-of-your-phoniebox>).
See also
As login credentials use the same username you used to run the installation with. The password is raspberry.
You can change the password anytime using the command sudo smbpasswd -a "<your-username>".