White House officials have revealed they can only hope Trump does not divulge sensitive secrets to his close friends when he speaks to them using the personal device.
Trump, who has two official phones altered by the National Security Agency, is reportedly ignoring warnings from aides that his personal smartphone is not secure, The New York Times has reported.
US intelligence agencies have cautioned Trump that Chinese spies have been listening in on his conversations and are exploiting the information they acquire as they navigate an ongoing trade dispute with the US.
The Chinese reportedly plan to use the information to persuade Trump to adopt policies more in line with their own interests.
Beijing hopes to influence Trump through the friends with whom they have heard him conversing.
Two of those individuals are Stephen Schwarzman, the CEO of private equity firm Blackstone Group, and former casino mogul Steve Wynn.
Mr Schwarzman has helped finance a master’s programme at Tsinghua University in Beijing.
And Mr Wynn has ties to China through a property he used to own in Macau.
A representative for Mr Schwarzman said the Blackstone CEO “has been happy to serve as an intermediary on certain critical matters between the two countries at the request of both heads of state”.
But Mr Wynn did not offer a comment.
Officials told the New York Times that Trump preferred to keep one personal phone because, unlike his two approved devices, he can store his personal contacts there.
A number of current and former senior intelligence officials spoke to the New York Times about the cybersecurity concern on the condition of anonymity.
They said they were not disclosing the details to undermine the President, but out of frustration with what they viewed as his casual approach to electronic security.
The officials said US spy agencies had learned China and Russia were eavesdropping on Trump’s phone calls from sources inside foreign governments.
They also intercepted communications between foreign officials, the individuals claimed.
Trump has been criticised for waging a trade war with the Chinese and for his bellicose rhetoric towards the Asian superpower as he relentlessly pursues his “America first” mantra.
The firebrand Republican escalated trade tensions between the world’s two largest economies when he slapped $50billion (£39billion) of punitive tariffs on Chinese imports this summer.
Beijing responded in-kind, placing an equal amount of sanctions in the form of new taxes on US products.
Trump added more tariffs to a further $200billion (£154billion) of Chinese imports in September, to which Beijing retaliated by introducing levies on an additional $60billion (£46billion) of US goods.