I found an Apple phone someone lost. How do I contact them?

You can try asking Siri who this phone belongs to.

It’s possible the owner may put it into lost mode so that it displays a message with contact information.

Short of that, there’s not much you can do. Turn it over to the lost and found at the place where you found it or to the local police. Apple won’t get involved. It would be a privacy violation for them to do so.

There is no way for you to contact them unless the owner provided the details on the Lock Screen. The owner is able to track their iPhone if they had Find My turned on, so the best option may be to leave it in an inconspicuous place so the owner can locate it themselves. If the battery is dead, maybe charge it up for them so they can continue to track it. I would not advise holding on to it as the original owner may think that you had stole it.