Radiation follows the inverse square law, while you're cellphone does not produce EM radiation which comes even close to natural high energy radiation sources you don't really put pulsars to your ear.
Additionally "natural" radiation is something you've evolved to coexist with. Take for example Uranium vs Plutonium, both are alpha emitters and they emit particles at nearly the same energy levels however that tiny energy difference results in very big difference in their effects on living tissue. The difference however cannot be explained by the power level difference alone, as both higher level alpha particles from natural sources as well as lower level alpha emissions from artificial sources showed a lower and higher amount of damage to nuclear material and cellular tissue general respectively.
And yes I am very well aware that alpha radiation isn't part of the EM spectrum as it's electron free helium nucleus, however it just shows that life evolved to be resilient to environmental sources of radiation be it high level particles like the nuclear decay of natural (existing since the 1st self replicating proteins occurred or even earlier if those had a replicating precursor) or high energy protons form the sun, or terrestrial and extra terrestrial sources of EM radiation.
