This card commemorates the game on April 17, 1976, when Mike Schmidt hit 4 home runs.
This was a wild game against the Cubs in Chicago. The Cubbies got off to a 12-1 lead by the third inning but the Phillies eventually won 18-16. Mike Schmidt was 5 for 6 with 4 home runs and 8 rbis. The game was tied 15 all after 9 innings. Schmidt had a 2 run homer in the tenth as the Phillies took an 18-15 lead. The Cubs managed another run but lost. The Phillies used 8 pitchers in the game including two guys who were normally starters in the 10th. Tug McGraw got the win even though he blew a save in the 9th by giving up 2 runs.
It would be nice to think that the picture of Schmidt on the card was from this game but since it was played in Chicago, no such luck. And I'm not sure what uniform the piece came from. I pretty sure the Phillies were wearing light blue away unis at the time.