Mr. Trump’s aides have repeatedly warned him that his cellphone calls are not secure, and they have told him that Russian spies are routinely eavesdropping on the calls, as well. But aides say the voluble president, who has been pressured into using his secure White House landline more often these days, has still refused to give up his iPhones. White House officials say they can only hope he refrains from discussing classified information when he is on them.

Mr. Trump’s use of his iPhones was detailed by several current and former officials, who spoke on the condition of anonymity so they could discuss classified intelligence and sensitive security arrangements. The officials said they were doing so not to undermine Mr. Trump, but out of frustration with what they considered the president’s casual approach to electronic security.

American spy agencies, the officials said, had learned that China and Russia were eavesdropping on the president’s cellphone calls from human sources inside foreign governments and intercepting communications between foreign officials.