There's a slim chance – emphasis on slim.

The Internet is by far the most likely way for your phone to be able to report its location. But for that, it needs to be turned on, and connected to a Wi-Fi hot spot, cellular data, or both.

The not-so-dependable backup?

If you had Find My Network turned on, and the phone has some battery charge left, it will send periodic Bluetooth beacons even when it is powered off. If another Apple device comes close enough to the lost/stolen phone that it can hear them, it may relay the location of the phone using its Internet connection.

This won't help if your phone is completely out of power, or if thieves have placed it in a Faraday cage type of bag that blocks radio signals (including Bluetooth signals) from getting in or out. And the chances of someone coming close to a stolen phone are lower than the chances of people with iPhones coming close to a lost AirTagged bag of luggage in a busy airport.