His professional career started off poorly, as he went 0–5 with a 5.52 earned run average for the New York–Penn League's Auburn Phillies in 1977.

[1] He debuted with the Philadelphia Phillies on April 13, 1980, pitching two scoreless innings out of the bullpen against the Montreal Expos.

On April 22, in his first and only at bat, Munninghoff hit a triple (and scored a run),[2] joining Chuck Lindstrom (1958), Eduardo Rodríguez (1973), and Eric Cammack (2000) as the only players to accomplish this feat in major league history.

After a poor outing against the Los Angeles Dodgers, in which he gave up a single, wild pitch and walked two (one of which occurred with the bases loaded) Munninghoff was reassigned to the triple A Oklahoma City 89ers.

In four relief appearances, Munninghoff posted a 4.50 ERA and did not have a decision or save, giving up three earned runs on eight hits and five walks while striking out two in 6.0 innings of work.