This kanji "ask" when I researched on it I found that the 門 part is a phonetic and this common with kanjis contain 門 .. but i found this site which says that this part 門 in kanji 問 not a phonetic but it has the meaning "to hide something behind the gate" and this meaning + ロ kanji meant that to "ask" about something which hidden behind the gate or the door.
Is this etymology right? And if it's right how did the author know this information about the meaning of "門 part using" in the kanjis?