The Phillies have not had a regular left-handed starter in their starting rotation since Adam Morgan was a regular in the role in 2016.   Phillies president Andy MacPhail mentioned in some comments after the regular season that the Phillies were in need of a left-handed starter, or so he wished. So now that the offseason is here it makes sense that the Phillies would be active in that market.  They appear to be already active.

Ken Rosenthal of The Athletic noted that the Phillies are in on starting pitcher Patrick Corbin in addition to Bryce Harper and Manny Machado:

The Phillies, operating in the sweet spot of burgeoning local TV money and few existing contractual commitments, are expected to be a major player for Machado or Harper and the top starting pitcher in free agency, Patrick Corbin.

Corbin is a two-time All-Star with the Arizona Diamondbacks who throws from the left side.  Most believe that he really came into his own in 2018, when he went 11-7 with a 3.15 earned run average.  Corbin struck out 246 in just 200 innings of work.

The Phillies' weakness of not having a lefty starter was shown at times this past season when left-handed hitting feasted on the Phillies righty pitchers.  And when the Phillies caught the eventual 2018 World Series Champion Boston Red Sox, the Phillies had three left-handed relievers who were firing on all cylinders and they held them at bay as they split four games.

The Phillies have also been preliminarily linked to Japanese lefty Yusei Kikuchi.