Most of the phones have likely ran out of battery. Also, there is a big chance that there are phones without victims. Not a good way to find people.
I would suspect that a notable number of phones are still on. As long as you don't turn the screen on and don't use any battery-draining apps, modern smartphones can easily have a battery life of a week or longer (even outside airplane mode).
Using that big screen, the quad-core CPU and the high speed internet are the battery drains, all of those are mostly in low-power mode while the phone is just in your pocket.
Who carries their phone in their pocket at home?
I miss the time when I needed to charge my phone once per two weeks (I used it infrequently).