Apparently, a short while after Ross left his position in the Obama administration, the White House made an unusual request to install a secure phone line in Ross' office at the Washington Institute. The secure line is known in Israel as a "red phone", which could be used to discuss confidential information without the risk of wiretapping.
In America, the term “red telephone” brings back memories of the Cold War and apocalyptic films such as of Dr. Strangelove. Guarded telephones in the U.S. Department of State as well as those in the White House are mostly white or gray. One of them sits in Dennis Ross’ office in his research institute, through which Ross receives updates regarding classified government information connected to his profession. There aren’t many independent researchers that receive such privileges.
I'm glad to provide an answer: because Dennis Ross is the Obama administration's chief interlocutor with the Israel lobby and Israel officials. Name me another country that has such power in the United States, or another (kind-of-former) official that has such influence despite having publicly adopted positions that are the opposite of those of the administration that he advises (on Iran, on settlements, on Jerusalem). That's because Ross is not the Obama administration's advisor on Middle East policy – he's one of the main conduits for the Israel lobby's to the administration.