I found someone's iPhone can't contact anyone

If it still turns on you can turn it on and see if it gives you a LOST MODE message with contact information for the owner. If they used iCloud / Find My iPhone to put it in "lost mode" there will be such a message. If it only asks for a passcode number or password you should turn it over to the nearest police station.

Other than providing the ability of the owner to place it in lost mode or remote-erase it if the owner chooses to use it, Apple doesn't get involved and can't help you find the original owner. Hopefully, the original owner will contact the police themselves to get their iPhone back.

Can you see the name of the cell phone provider? When this happened to us we went to the carrier’s retail store in case they went there and they did. They were able to tell us what kind of case it was in.

Take it to the police in the area you found it.

if you can’t access phone to contact owner, then don’t worry they will probably be contacting you, locating their phone location real quick Lol