small phone simbol in facebook chat?

[Manoj Chamikara *McK*]

Hi friends need some help
i'm log in to facebook using my pc my friend log in to facebook using his i phone so Small Phone Symbol In his chat bar when he go offline
i need to know when he switch off the phone that symbol also lose or not ? what is the reason that symbol lose ?
thank in advance

[Terence]

when he logged off the Facebook and after two days he didn't logged back then symbol will remove