HONG KONG— Foxconn Technology Group is scrambling to contain a weekslong Covid-19 outbreak at an iPhone factory in central China, trying to appease frightened and frustrated workers during a crucial period for smartphone orders. In Foxconn’s main Zhengzhou facility, the world’s biggest assembly site for Apple Inc.’s iPhones, hundreds of thousands of workers have been placed under a closed-loop system for almost two weeks. They are largely shut off from the outside world, allowed only to move between their dorms or homes and the production lines.