phase-in noun 1phase in verb 1forms 4 noun1 •A gradual introduction. phase in verb1 •To introduce (something) little by little, either via discrete phases of increase or (by extension) by continuous gradations; to introduce in phases, or as if by phases (gradually); to begin (something) gradually.The government will phase in the new education system over a period of three years.The program phased in last year. formsphased in · phasing in · phases in · phase-ins
