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.
I don’t want to encourage paranoia here but “off” does not mean “off”. Modern phones are almost never actually “powered down”. If you’re paranoid, turning your phone off is not enough. Leave it behind.
(Also a gap in your phone’s location history can also be used against you, fwiw.)