so many valid answers are not accepted.
phone = telephone
out of charge = out of battery = flat
Tried "run out of juice" and got wrong answer, i guess the developers did not into idioms :-/
Idioms are actually accepted but it is not the main purpose. Haha. So just report the translation and hope it gets accepted.
"My phone's battery is dead " is also correct in english but not here
I would never say 'my phone is out of charge' although gramatically correct it would not be a very common way to say this.
My phone is lowbatt