It’s really about whether it’s ionising radiation or not, being “too close” isn’t a real concern for phones and wifi.
Discussion
Ionizing radiation is proven to be bad. I think most people discuss non-ionizing radiation in these topics. You can have non-ionizing radiation that enters the skin and blood with an amount of energy big enough to cause electronic excitation. That can be used for the good and the bad. See therapeutic photomedicine, for instance, where people beam the body with visible light at such a high level that it can temporarily cut neuron transmission and block pain.