He uses the device mostly to tweet from his private Twitter account, according to Maggie Haberman, the story's author. The report notes that Trump uses the phone "to the protests of some of his aides."
Trump's reliance on his personal Twitter account for statements has led to security concerns since he was elected. The president's tweeted messages have moved financial markets and prompted responses from foreign governments.
It is unclear what security measures specifically are in place for the phone.