Beijing’s widening curbs on iPhone use by government staff raised concerns among U.S. lawmakers on Thursday and fanned fears that American tech companies heavily exposed to China could take a hit from rising tensions between the countries. Apple closed down 2.9% Thursday — its worst two-day percentage decline since November — after news that Beijing has told employees at some central government agencies in recent weeks to stop using their Apple phones at work. Several Wall Street analysts said the curbs show that even a company with a good relationship with the Chinese government and a large presence in the…