I’m always stunned when watching a movie/TV show in which a criminal makes a final call, then breaks the phone and throws it away in order to get rid of incriminating evidence. Yeah, sure, burner phones exist to be disposed of, but why break them? Your telco has a record of the phone call and if the police found the wreckage (your telco also knows which radio mast you have been connected to, when making that final call), they could desolder the internal storage from the mainboard - NAND flash chips can be quite resilient. They are also very bad at actually erasing data (when you delete a file, the operating system just marks the storage space as available again. If you truly want to get rid of a file, then you would first have to overwrite it with random garbage. However, writing to NAND flash is slow and wears the chip down - the controller tries to avoid that).
Yeah ok, that’s a problem for criminals, not law abiding citizens. You have nothing to hide - except maybe the credentials for your Google account, online banking…
Something, one should probably keep in mind when selling a used phone: doing a factory reset means all data on the phone is lost — unless the new owner has specialized equipment.