Privacy advocates got access to Locate X, a phone tracking tool which multiple U.S. agencies have bought access to, and showed me and other journalists exactly what it was capable of. Tracking a phone from one state to another to an abortion clinic. Multiple places of worship. A school. Following a likely juror to a residence. And all of this tracking is possible without a warrant, and instead just a few clicks of a mouse.
A Faraday cage is supposed to be grounded, so aluminum foil isn’t the same thing. Maybe you could turn the phone off, wrap it in foil, and then place it upon a conductive metal surface that is grounded, such as a 240v kitchen appliance