Since this word is made up of a single kanji, it should use the kun'yomi reading. Numbers, as you know, are the exception to this rule. They usually use the on'yomi reading, and the on'yomi reading is the one you learned along with this kanji, meaning you should be good to go!
Is Yamamoto’s phone number 612-7736?
Let's meet at Mt. Fuji at six o'clock.
Six times six is thirty-six, right?