Other forms: phases; phased; phasing
A phase is a particular period of time, like someone whose "teenage rebellion" phase lasts well into her thirties.
The word phase can mean a stage in a person’s development or a step in a process, such as “the next phase in the Interstate 57 project.” Phase can also be a verb, usually followed by in or out, to mean slowly introducing or getting rid of something. For example, your school might phase in a new rule or phase out an old one, as new students arrive.