Well, a decent way to differentiate these would be to put the phone in airplane mode, and then you'd see what RF was significant and not.

And then after that, a further level of differentiation would be to take the phone out of airplane mode, but remove the SIM card.

I feel like those different states would be worth comparing...

I agree, that would be interesting. Removing the SIM would not prevent the phone from communicating using GSM (emergency services, should still work). But I guess it would probably prevent data (EDGE, 3G, 4G etc.) from being active. Also I guess the internal processor in the SIM is fairly low frequency (5 MHz I think) so the detector will probably be more sensitive to this than it is to the internal CPU in the phone.

thanks for the tip. Let's see where this project goes from here. I'm by no means an electronics engineer so any advice to get rid of incorrect readings or misinterpretation is more than welcome.

Yeah, the circuit is very sensitive and noisy indeed, even my hand touching the phone would change the light pattern. I would love to revisit this project with some proper electronics knowledge. I'm open to collaborations ;)