In May 1956 he signed for Celtic, the team his elder brother John had previously captained. He made his debut in a 2–1 Scottish League Cup win against Aberdeen. Later that season, McPhail scored twice in the League Cup final, helping Celtic lift the trophy for the first time. The following year, he starred in the Celtic team that played fierce Old Firm rivals Rangers in the final of the same competition. The match, referred to by fans in poem and song as ""Hampden in the sun"", resulted in a record 7–1 victory to Celtic, with McPhail scoring a hat-trick.