I leave my iPhone charger plugged in all day. Does it draw current when I'm not charging my phone?
If the USB cord is not plugged into anything on the other end it should not be drawing any power that would be worth speaking of.
However if you are talking about the USB charger box that converts a normal power outlet to USB power to charge your iPhone then yes, those do draw power as long as they are plugged in. You can tell as they get very warm even when not charging.
It is recommended to unplug any electronics when they are not in use to save power, however I do not do this unless I am not using it for a few days.
Yes it does, it has a transformer in it where the current passes true at all time as long it is plugged in to a socket.
Since it is in idle mode it might draw some micro amps.
To put it in prospective 1 Amp = 1000 mA
and 1 Milli Amp = 1000 uA (micro amps)
So it is drawing 10-6 Amps :) (one millionths of a Amp)
So from consumption it is to small to even consider.