Ahsanallahu ilaykum. In conditions of Wudu', why does intention of passing wind nullify the wudu but not picking up the phone? Does picking up the phone not fall into discontinued Niyyah?

Well, passing wind nullifies wudu, but picking up a phone doesn't. When you intend to break your wudu, it is different than when you don't intend to break it. In this case, you intend to pick up the phone and carry on with your wudu; that is why.