These are different levels of privacy invasion, at least in the US.

Going through a phone to check what you are thinking / saying is seen as more intrusive. So even in a stop and frisk, going through someone's phone would not generally be justified.

The rules here are very clear. In particular, even in a terry stop police generally are not authorized to seize / search your cell phone. But they can pat down your outer clothing for weapons.

That's how it works with most things. If you ride somewhere with a tank and shoot at something, it makes a difference if you're "defending your country" vs "invading".

If you shoot at someone, it makes a difference if your goal is to stop him from shooting you, or if you're trying to kill him to steal his car.

Ends justify means. Though ends need to be justified, too.