https://www.theguardian.com/technology/2018/may/22/donald-trump-shuns-white-house-iphone-security-inconvenient-reports-say [theguardian.com]
While his call-capable iPhone is issued by White House staff and is swapped out “through routine support operations” to check for hacking and other security concerns, Trump has resisted attempts to do similar for as long as five months with his Twitter phone, saying it was “too inconvenient”.
A US president has the power to override White House policy and disregard advice, but given that the devices and systems they use are prime targets for foreign intelligence agencies, doing so can pose significant US national security risks.