An Essex County school district is delaying a pilot program that would have had students at four schools locking up their cell phones. The K-12Montclair Public Schools district announced in June a partnership with Yondr, a San Francisco-based company whose best-known product is a lockable pouch in which a cell phone is placed, rendering it unusable until tapping it on an unlocking base. It would have began when classes in Montclair resume Sept. 5. However, Montclair interim schools schools superintendent Damen Cooper said at a school board meeting Tuesday he is postponing the pilot program for…