Wrapping your phone in foil is a good way to literally turn it into a burner phone. You'll fry the phone due to overheating. Overheating will also drain the battery and cause the phone to run poor and unstable (much like with computers when they overheat).

Using duckduckgo.com doesn't anonymize you. They just don't place tracking ads on their site is all. You're still traceable. You can use something like TOR to help anonymize yourself though. Still, you're not 100% anonymized. Nothing will 100% anonymize you on any device,y especially cellular devices.