Idioms – Idioms for a Person Who Spends Too Much Time on the Cellphone

A common phrase is "Yes-man", a person who follows someone around and gives "advice" by always agreeing with their idol. It's a derogatory word; one that the follower should be ashamed of - but they may not believe that that is what they are doing - they may simply believe that everything the person says is golden.

Another colloquial word is "boot-licker"; and that's an even more distasteful word (exactly as it sounds!)

But a proper English word would be "sycophant":

a person who praises powerful people in order to get their approval.

This is also not a nice word - but I believe that it is the English word closest to what you are after.

You're very close. The colloquial expression is actually "to hang out":

hang out: to spend a lot of time in a place or with someone

Related to your question, I could say:

He spends way too much time hanging out on the Internet.

He hangs out on the internet way too much.

Although this is not in the dictionary definition, these sentences also imply that he is not achieving anything useful during this time, that he is wasting time.

He wastes way too much time hanging out on the Internet

There are numerous other ways to say this: slack off, fritter away (time), screw around, as well as other, less "polite" expressions.