I think "Phone Idle" refers to the state when the LCD (and possibly wifi) is turned off. In this state, the processor is still running and consumes power (and you can use the e-ink side). Whatever battery is consumed during this state, the battery stat meter will call "Phone idle" I am not sure how background apps affect the battery usage in this mode. I find that if I fully charge the eDGe and then turn off the LCD and wifi, it will last about 10 hours before draining the battery.