phase-in

The next phase of the trial consists of vaccinating Ebola workers on the front lines.
The Race for the Ebola Vaccine|Abby Haglage|January 7, 2015|DAILY BEAST
This is a guy who has his son-in-law clean his eyeglasses, for crying out loud.
Will Chris Christie Regret His Cowboy Hug?|Matt Lewis|January 5, 2015|DAILY BEAST
Her travel clique has been known to arrive at an airport, bags packed, passport-in-hand, within hours of spotting a deal.
‘We Out Here’: Inside the New Black Travel Movement|Charlise Ferguson|January 4, 2015|DAILY BEAST
Earl Spencer adds, “Effectively, my great-grandfather sold his children to his father-in-law.”
The Real-Life ‘Downton’ Millionairesses Who Changed Britain|Tim Teeman|December 31, 2014|DAILY BEAST

The lack of a gun is not likely to be a major problem for close-in air-to-air dogfights against other jets.
New U.S. Stealth Jet Can’t Fire Its Gun Until 2019|Dave Majumdar|December 31, 2014|DAILY BEAST
But between the phase of schooling and the phase of adult learning there is an intermediate stage.
The Salvaging Of Civilisation|H. G. (Herbert George) Wells
Such throats are trying, are they not?In case one catches cold; Ah, yes!
Boys and Girls Bookshelf; a Practical Plan of Character Building, Volume I (of 17)|Various
The commander-in-chief still kept him attached to the headquarter staff, and constantly employed him on special service.
Napoleon's Marshals|R. P. Dunn-Pattison
So far Murat had always held subordinate commands; his great ambition was to become the commander-in-chief of an independent army.
Napoleon's Marshals|R. P. Dunn-Pattison
Their jurisdictions overlapped and the Gascon would play second fiddle to no one save to his great brother-in-law.
Napoleon's Marshals|R. P. Dunn-Pattison

British Dictionary definitions for phase-in

phase in

verb

(tr, adverb) to introduce in a gradual or cautious mannerthe legislation will be phased in over two years

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Idioms and Phrases with phase-in

phase in

Introduce one stage at a time. For example, New technology must be phased in or the office will be overwhelmed. The antonym is phase out, meaning “to bring or come to an end, one stage at a time,” as in The department is phasing out all the older computers. [Mid-1900s]