White House officials say they are hoping that Trump doesn't divulge any sensitive secrets to the friends with whom he speaks.
The New York Times reports that American agents believe China is in fact listening in to the President's private calls.
"I only use Government Phones, and have only one seldom used government cell phone", he wrote.
Despite repeated requests by intelligence advisors, Trump seems to continue using the phone, which might one day cost him dearly not only to himself but also to national security too, reported The New York Times.
The newspaper cited anonymous officials who said China and Russian Federation had listened in to Trump's frequent phone calls with friends and allies made over his iPhone, using the information gleaned to shape interactions with the US.
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She continued, "I've never been a "pc" kind of person - but I understand that we do need to be more sensitive in this day and age".
The President has been loath to part with his iPhones, which he uses to tweet out his responses to the latest news.
We have come to understand that Donald Trump, after dragging his feet for a year after presiding over the Oval Office, finally gave up his personal Android phone and got himself custom-made iPhones, which as per reports has no camera to take pictures and no microphone, but only receive texts from secured government servers.
They say they learned from sources inside foreign governments, and through intercepted communications between foreign officials, that Trump's phone calls were being tapped.
Through its efforts, China reportedly identified Blackstone Group chief executive Stephen Schwarzman, who has ties to Beijing's Tsinghua University, and former Las Vegas casino mogul Steve Wynn as potential targets in an influence campaign to curb the ongoing trade war with China. It is unclear from the report whether President Trump makes calls from this third phone.
"Many of those Mr 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", the daily said.
Russia's operation is believed to be less sophisticated because of his "apparent affinity" for President Vladimir Putin, a former official is cited as saying.