Maybe it has something to do with the adaptive power controls on most modern phones. They throttle back once the connection has been made. The only other explanation I can think of is if the phone is perhaps tethered via a USB connection. That might drop the levels way down since it's wired and not wireless.

I'd do a little light reading on SAR/EMF here-

http://www.emfexplained.info/?ID=25585

http://www.mmfai.org/public/sar.cfm