Mormon teen-agers have submitted a petition to the Phoenix division of Dillard's department stores asking for more modest clothes. They say it's getting more and more difficult to buy clothes that don't reveal cleavage, bellies or lower backs. The petition -- signed by about 15-hundred teens -- asks retailers to start selling fashionable clothes that cover the midriff, bust, shoulder, back and upper legs. Kent Burnett, who heads Dillard's Phoenix division, says "We certainly hear them and we're concerned about it." The petition drive was organized by the Mormon church.