According to The New York Times, the Chinese are regularly listening to Donald Trump’s cellphone calls (Warning: source may be paywalled. If so, try this alternative source). While he has two NSA-hardened iPhones, and a secure landline, he insists on using a consumer-grade iPhone — even while knowing he’s being eavesdropped upon — because it has his contact list on it.
“White House officials say they can only hope he refrains from discussing classified information when he is on them,” reports the New York Times. But, officials were also confident that “he was not spilling secrets because he rarely digs into the details of the intelligence he is shown and is not well versed in the operational specifics of military or covert activities”; in other words, security through ignorance.
The article mentions the rationale is to be able to listen to his calls to find out what and whom influences him, and that the Russians also listen in, albeit with less frequency because of his unique relationship with Vladimir Putin.