I use the setting "existing access via WLAN" under Internet > Access data so that there is no physical connection between the Internet router (Speedport) and the home network (FB4060). This should also work if the Speedport is replaced by a mobile hotspot.
Supplementary: The home network has a different SSID than the Internet router, so the FB does not serve as a repeater, but creates its own self-contained WLAN.