Between the 1930s and 1950s, at a time when the Communist Party had sway over much of the left in the United States, the Jacobsons were associated with a radically democratic current of the socialist movement which rejected Stalinist bureaucratic collectivism and understood the Soviet Union to be a perversion of socialism because of its lack of workers' control over industry and society.
They were founding members of the Independent Socialist League, for which she was briefly the Manhattan organizer and which espoused Third Camp socialism.
As the ISL and its leader Max Shachtman began to turn, in their view, toward the Right after 1956, the Jacobsons persisted in what they perceived to be their left-wing democratic socialism, like Hal Draper, and declined to follow Shachtman and his circle, who, they thought, became virtually or wholly neoconservative.
"It was Phyllis who handled the day-to-day work of the journal," wrote a New Politics editorial board member in an obituary.
Some though that she, unlike Julie, was the real schmoozer, with a rollicking laugh so infectious that rare indeed were those who could resist joining her.