That would go against most public accounts of how Trump has been using his phone for tweeting.
For one thing, Obama's personal account (i.e. not @POTUS, but @BarackObama) explicitly says in its profile: "This account is run by Organizing for Action staff. Tweets from the President are signed -bo. [0]
No such disclaimer has been made about Trump's account, which tweets with the same characteristics and tone as it did well before his current presidential campaign [1]. You're right, though, that Trump's team does tweet for him on occasion. Either that, or Trump, who is famously not a computer user, has mastered the art of using two different mobile operating systems [2]
