So who is this team’s sixth starter?

With Roy Halladay feeling “lethargic,” this has suddenly become an important question at Phillies camp.

At this point of spring training, the two most likely candidates are a pair of veteran righthanders, Aaron Cook and Rodrigo Lopez.

As fate would have it, both were on the mound yesterday against the Pittsburgh Pirates. Cook pitched scoreless ball for three innings, Lopez for two in a 2-1 win over the Pirates.

The Phillies signed both pitchers to minor-league deals because it is crucial for a team to have starting pitching depth. The Phils have learned that untold times in recent years, including 2009 when Lopez was signed to a minor-league deal in March and came to the majors later that season and won three games. The Phils, of course, went to the World Series that year. The 2011 season offered another example of the importance of starting pitching depth when Vance Worley plugged the hole for injured Roy Oswalt. He won 11 games during that 102-win season and finished third in the NL rookie of the year voting.