The Federal Communications Commission took another big step toward a deregulated interstate long-distance phone business and proposed to loosen rules on AT&T because the onetime monopoly company now faces ``significant competition.'' The commission, in a 4-0 vote Thursday, adopted a staff proposal that, if finally approved, would give the American Telephone & Telegraph Co. the freedom it says it needs to maneuver against some 500 long-distance companies in the $55 billion long-distance marketplace.