My phone got hacked once. They were able to turn on/off my wifi at will, without me knowing it. I know, because I could see them doing it. But what I saw on my screen and what was happening inside my phone don't necessarily correlate. But I know they did it, because I could see that two of my phones repeatedly toggled to on and when the suspect made his move to attack and was tracking me my phone settings showed that wi-fi was off.
Seriously, how can you not get this???
Oh, I get THAT, I am not saying that hacking cannot occur, any more than hacking any computer.
But every hack I am aware of requires both - that the number is alive, and that it has an internet connection (and that normally NOT from behind a router, IOW, a cellular internet connection...)
AFTER being hacked, of course you are pwned. Of course the connection can be hidden.
PRIOR to the hack, put it in airplane mode, and it is a virtual brick as far as hacking it goes.
Shut off WIFI or at least promiscuous WIFI, so you don't automatically log into public networks and you are probably pretty safe.