transitive verb
1. : to eliminate as a phase of an operation or system
2. : to discontinue the practice, production, or use of by phases
3. : to complete (as an operation or activity) by planned phases
phase out an advertising campaign
intransitive verb
1. : to stop production or operation by phases (as by discontinuing the manufacture of component parts exceeding the quantity required for the assembling of items scheduled for completion)
the company has phased out of the truck manufacturing business
2. : to pass from one phase into another
groups have phased out into a new command