The team forms, but nobody says the comics' rallying cry "Avengers assemble". Kevin Feige felt it did not fit the film, and Age of Ultron (2015) cut Cap off mid-line.
With every returned hero gathered behind him, Steve finally says "Avengers... assemble" before the charge against Thanos's army.
Marvel held the comics' most famous line back for seven years and used it once the full team was assembled.