Chinese shipments of Apple Inc.’s iPhone and other mobile devices to the US dived to their lowest levels since 2011 in April, underscoring how the threat of US tariffs choked off the flow of big-ticket goods between the world’s two largest economies.Smartphone exports slid 72% to just under $700 million last month, sharply outpacing an overall 21% drop in Chinese shipments to the US, detailed customs data showed on Tuesday. That highlighted the way the Trump administration’s tariffs campaign — p...