phase in   (TTS發音)

introduce sth. gradually or in stage 逐步採用；分階段引入

    They phased in the new course by accepting just five students in the first year， and ten in the second. 他們逐步發展新專業，第一年只收5個學生，第二年收了10個學生。

    They've decided to phase the new techniques in. 他們已決定逐步引進那些新技術。