Indeed, if you have a second cell modem or smartphone, the modem can connect to the cellular network and provide an IP over Wifi, and the smartphone can use wif

Indeed, if you have a second cell modem or smartphone, the modem can connect to the cellular network and provide an IP over Wifi, and the smartphone can use wifi to connect to it. Thus the smartphone is protected by its OS's firewall and any compromises stay on the cell modem, the same way they do with home internet connections.