The Phillies selected Lazar's contract from Triple-A Lehigh Valley on Friday.
The 25-year-old will join Philadelphia for his first look in the big leagues, taking the roster spot of Kolby Allard, who was optioned to Triple-A in a corresponding move. Lazar has pitched well for Lehigh Valley this season with 10 saves and a 2.40 ERA, 1.03 WHIP and 35:9 K:BB across 30 innings.