"Bind off 5 (5, 6, 6) stitches for neck, finish row. Continue in St st, dec 1 st at neck edge every row 2 (3, 3, 4) times – 9 (10, 11, 12) sts. When piece measures same length as Back, bind off."
The pattern wants you to bind off 5 sts for the neck and then finish the row by continueing the stockinette stitch pattern (since you do this on the WS row, you're purling). Then decrease one stitch at the neck edge on the next row and the row after that. You'll have 9 sts remaining on the needle.