For a non-functioning one it's quite simple. There are dummy phones for most models that are to be used in e.g. store displays. You can get those for ~€5-10 on ebay. They are just a shell and nothing else. Alternatively you can just take an old phone and remove all the content, though the dummy will have more space inside, since you'll have to leave the screen in if you take an old phone.

Then you need an USB killer. You can find them on the usual online shops. You'll need to find one that is as flat as possible, the other dimensions don't really matter.

This is now the only somewhat tricky part: You will need to remove the USB port from the USB killer (unless it already comes with an USB C port), take an USB C socket (there are ones on a small breakout PCB), solder the socket to the killer and mount the socket inside the dummy/phone in a way that it sits at the right place and can easily be used without falling off.

I would not use sand to make the phone heavy, as it's probably not that easily contained and it would also not be quite as easy to make it not flow around and sound like a salt shaker. Instead use fishing weights and glue them into the case.

Now, don't forget, this is all hypothetical. Nobody's going to ever, ever build anything like that, and I wouldn't have ever told anyone how to do this if I thought that anyone would do it.

Honestly, just pack something with a USB port, and no descriptor. No labels, no nothing. Hell, make it out of a little hobby box container and put a port on it. Done.

Some dumb ass will plug it in to see what it is.

Remember, police have a maximum intelligence limit for hiring, or so its rumored, and if you've dealt with many cops, well.... seems pretty fair.

Intelligent people ask questions. Fascism doesn't like people asking questions.