Just where do you keep your mobile phone when you're broadcasting, i.e. sending out? Mobile phone radiation is very low power, but I suspect sustained use can be damaging.
I recall hearing about police back in the 1930s, 40s and 50s becoming sterile because the radio operator in the back on the police cars of those days used to sit over the top of the radio transmitter. In those days, of course, it was HF radio and far more power was needed.
I know radio aerials can burn terribly. I experienced same when I copped about 2 amps through my hand whilst cleaning soot of an radio transmitter's insulator. However, this jolt/burn came from a 500 watt transmitter.
Still, to be sure that you're not physically damaged by a mobile phone, I'd say use it sparingly, or else get yourself a set of headphones and keep the mobile clear of any place you think it might cause you harm. However, that said, I wouldn't concern myself too much. I think you'd need an awful lot of exposure before any real harm would be done from such a small wattage.