Justin Sullivan/Getty Images
According to Nicholas Carlson's biography of Yahoo CEO Marissa Mayer, Sandberg left a voicemail on Tumblr CEO David Karp's iPhone after reading reports about the deal. In the voicemail, all Sandberg asked was for Karp to call her back.
But the Yahoo-Tumblr deal was almost finished by then, and Karp and the Tumblr board didn't want to risk a bidding war that would cause Mayer to pull out. As part of their agreement while working on the acquisition, Karp and the Tumblr board had to tell Mayer that Sandberg had called.
According to Carlson, this encouraged Mayer to get the deal finished faster. In the end, the Tumblr board decided to accept Yahoo's $1.1 billion offer.