"... even though the target of the surveillance effort was almost certainly the president himself."
Why would anyone bother to target his phone? Any information on his phone will be stuff that he is posting to Twitter, for the world to read.
It seems more likely that the Israelis were providing information to the US administration that their own intelligence agencies could not legally collect. A bit like when Margaret Thatcher had the Canadians use Echelon to spy on some of her cabinet ministers whom she believed were disloyal. The Canadians provided intercepts that showed her suspicions were correct.