NEW YORK — At the gate, guests slipped their phones into little cloth bags, putting them away for the evening. As the sunlight faded on a cobblestone street, more than 200 students from New York University gathered at a table nearly as long as the city block. It was cold — so cold that they ate wrapped in plush blankets and clutching handwarmers — but they leaned in to talk with strangers, laughing and trading stories.