WASHINGTON >> When President Donald Trump calls old friends on one of his iPhones to gossip, gripe or solicit their latest take on how he is doing, U.S. intelligence reports indicate that Chinese spies are often listening — and putting to use invaluable insights into how to best work the president and affect administration policy, current and former U.S. officials said.

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.

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 Trump, but out of frustration with what they considered the president’s casual approach to electronic security.

U.S. 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.

The officials said they have also determined that China is seeking to use what it is learning from the calls — how Trump thinks, what arguments tend to sway him and to whom he is inclined to listen — to keep a trade war with the United States from escalating further. In what amounts to a marriage of lobbying and espionage, the Chinese have pieced together a list of the people with whom Trump regularly speaks in hopes of using them to influence the president, the officials said.

Among those on the list are Stephen A. Schwarzman, the Blackstone Group chief executive who has endowed a master’s program at Tsinghua University in Beijing, and Steve Wynn, the former Las Vegas casino magnate who used to own a lucrative property in Macau.

Russia is not believed to be running as sophisticated an influence effort as China because of Trump’s apparent affinity for President Vladimir Putin, a former official said.

China’s effort is a 21st-century version of what officials there have been doing for many decades, which is trying to influence American leaders by cultivating an informal network of prominent businesspeople and academics who can be sold on ideas and policy prescriptions and then carry them to the White House. The difference now is that China, through its eavesdropping on Trump’s calls, has a far clearer idea of who carries the most influence with the president, and what arguments tend to work.

The Chinese and the Russians “would look for any little thing — how easily was he talked out of something, what was the argument that was used,” said John Sipher, a 28-year veteran of the CIA who served in Moscow in the 1990s and later ran the agency’s Russia program.

Trump friends like Schwarzman, who figured prominently in the first meeting between President Xi Jinping of China and Trump at Mar-a-Lago, the president’s Florida resort, already hold pro-China and pro-trade views, and thus are ideal targets in the eyes of the Chinese, the officials said. Targeting the friends of Schwarzman and Wynn can reinforce the views of the two, the officials said. The friends are also most likely to be more accessible.

Officials said the president has two official iPhones that have been altered by the National Security Agency to limit their capabilities — and vulnerabilities — and a third personal phone that is no different from hundreds of millions of iPhones in use around the world. Trump keeps the personal phone, White House officials said, because unlike his other two phones, he can store his contacts in it.

Apple declined to comment on the president’s iPhones. None of them are completely secure and are vulnerable to hackers who could remotely break into the phones themselves.

But the calls made from the phones are intercepted as they travel through the cell towers, cables and switches that make up national and international cellphone networks. Calls made from any cellphone — iPhone, Android, an old-school Samsung flip phone — are vulnerable.

The issue of secure communications is fraught for Trump. As a presidential candidate, he regularly attacked his Democratic opponent, Hillary Clinton, during the 2016 campaign for her use of an unsecured email server while she was secretary state, and he basked in chants of “lock her up” at his rallies.

Intercepting calls is a relatively easy skill for governments. U.S. intelligence agencies consider it an essential tool of spycraft, and they routinely try to tap the phones of important foreign leaders. In a diplomatic blowup during the Obama administration, documents leaked by Edward J. Snowden, a former contractor for the NSA, showed that the U.S. government had tapped the phone of Chancellor Angela Merkel of Germany.

Foreign governments are well aware of the risk, and so leaders like Xi and Putin avoid using cellphones when possible.

President Barack Obama was careful with cellphones, too. He used an iPhone in his second term, but it could not make calls and could receive email only from a special address that was given to a select group of staff members and intimates. It had no camera or microphone and could not be used to download apps at will. Texting was forbidden because there was no way to collect and store the messages, as required by the Presidential Records Act.

“It is a great phone, state of the art, but it doesn’t take pictures, you can’t text. The phone doesn’t work, you know, you can’t play your music on it,” Obama said on “The Tonight Show Starring Jimmy Fallon” in June 2016. “So basically, it’s like — does your 3-year-old have one of those play phones?”

When Obama needed a cellphone, the officials said, he used one of those of his aides.

Trump has insisted on more capable devices, although he did agree during the transition to give up his Android phone (the Google operating system is considered more vulnerable than Apple’s). And since becoming president, Trump has agreed to a slightly cumbersome arrangement of having two official phones: one for Twitter and other apps, and one for calls.

Trump typically relies on his mobile phones when he does not want a call going through the White House switchboard and logged for senior aides to see, his aides said. Many of those Trump speaks with most often on one of his cellphones, such as hosts at Fox News, share the president’s political views, or simply enable his sense of grievance about any number of subjects.