When you lose internet, you get a ! next to the bars (at least I have on my last few androids). Usually I also have no bars when I lose internet, but sometimes I've got coverage without data flow.

You can have full bars and no internet when jammed in a crowded space with full pipes. Just because the PHY is linked doesn't mean you have internet.

Wish Apple would do that. It’s kind of a guessing game.

You should but you don't always