Say radar works at a frequency of 1 GHz. RECCO uses a small electronic circuit to generate a harmonic (integer multiple of that signal) which goes back to the sender.
so you are the asshole that will kill someone because you value a gopro over a life. while they are frantically trying to locate a buried human, they will accidentally be following the signal from your lost cellphone.
A recco is used when the person is presumed dead and their beacon batteries have died. Otherwise they use a beacon to.locate the person because a beacon is not nearly bulky as a recco locator.
i thought it was a pretty good explanation of why they sometimes use reccos and sometimes use beacons.
a cell phone signal will not interfere with a recco locator. the reason it detects these electronic devices is because the batteries in them are mostly metal, and reflect the signal.