It depends.
If you want to be shielded from high voltage high frequency electro magnetic waves then a Faraday cage may work. But if you put your cellphone in a cage, and let someone else call you...
Well, give it a try and let me know the result. :-)

For high voltage there is a skin-effect and THAT travels on the outside of a cage to the ground.
But what happens with the cellphone signals is not explained by science as far as i know.

So how FCC can claim to make a difference between safe or unsafe cellphone signals is beyond me.
Before you can make that claim you have to be able to measure anything. And my experiment above shows you that there is a massive gap in science. I think i know a part of the answer, but i'm not a big name scientist. And the little part I know for sure that's how I managed to get to this experiment.

I have viewed the entire MIT course on this topic but could not find anything in there that could explain this. https://archive.org/details/MIT8.01F99
Some subjects get close but they are about high voltage, and that's where a cage works just fine. :-)
Once the rest of internet discovers this article then some people will most likely ridicule me. Yet my experiment will still work.

Let the bullshitters reveal themselves.

Come kitty kitty.... it's a challenge. Not a textbook recital game.