phase in

from WordNet (r) 3.0 (2006)

phase in
    v 1: introduce gradually [ant: {phase out}]

from The Collaborative International Dictionary of English v.0.48

Phase in \Phase" in`\ (f[=a]z" [i^]n`), v. t.
   To begin an activity or to incorporate new elements or
   replace older elements of an activity in steps, or by
   degrees.
   [PJC]