USB tethering to connect Linux to Android
Tethering doesn't provide access to device's storage. It simply establishes a network between the host (mobile) and client (PC) where PC can access internet, if available. If you need storage access, try MTP or ADB or network based file access (WebDAV, FTP, SSH, etc.). I do not know much about setting-up MTP on Debian but the rest alternatives are covered in my answer here.