Could be, plawrence. Another possible explanation: The reason Phillips was of use to the Corleones was that he was on the NYPD's "Mob Squad," or its equivalent in that era. Since his nominal job was to help the cops (not the Corleones), and since he supposedly knew more about the Corleones than other detectives, he was detailed to go to New Hampshire to lean on Kay and her family. He really had no choice: he couldn't very well refuse without raising questions about his loyalties. In short: he had to do it, but I don't think that it meant he'd turned on the Corleones.