SOL LEWITT and SUMMER GROUP SHOW Pace Wildenstein until August 25 (534 W. 25th Street, between Tenth and Eleventh Avenues, 212-929-7000). PHONG BUI Sarah Bowen until August 7 (210 N. 6th Street, between Driggs and Roebling Avenues, Brooklyn, 718-302-4517).   For all his extreme, at times arid, cerebrality, Sol LeWitt has a soft spot. The … Continued