John J. Phelan Jr., a former chairman of the New York Stock Exchange who introduced computer technology to the Big Board in the 1980s and was widely praised for his calming response to the stock market crash of October 1987, died on Saturday in Manhattan. He was 81. After the 1987 crash, which shook investors' confidence in financial markets, Mr. Phelan coolly resisted calls to close the exchange, fearing that it would breed further panic. He rang the closing bell himself. "He deserves eternal credit for that,"Felix G. Rohatyn, a longtime investment banker who helped save New York from bankruptcy...