phasephase1 /feɪz/ noun [countableC]1a part of a process of development or growthThe company is conducting phase 1 and phase 2 clinical trials with the drug.
The consortium will pay $92 million for insurance to cover the construction phase of the project.
2in phase/out of phase (with something) if something is in phase with something else, it is happening in a similar or related way at the same timeBritain’s economic cycle has historically been out of phase with those in mainland Europe.