"My phone is running out of juice"没错，但这属于俚语，并非正规的说法。 首先，光手机有很多种说法，比如cellphone, mobile phone, mobile等。 “我的手机快没电了”最准确的说法说"My mobile phone is running out of power"。

I can't see anything wrong with this sentence "“我的手机快没电了”

My phone is running out of power

My cellphone is out of power