|to phase sth in / to phase sth out / a phase
A phase is a period of time, especially a period in which one part of a process takes place. So a company may go through ‘a growth phase’ or ‘a difficult phase’, for instance. It’s also common to use it as a verb – especially for changes in organisations or society. So, when a new system is phased in, it means it’s introduced gradually, step by step. For instance, in many countries, digital television is being phased in. This means that, for the moment, the older televisions still work, but they are slowly being replaced. You could also say that these older televisions are being phased out. Another example is the phasing out of old coin-operated parking meters and their gradual replacement with the new ones which you can charge from your mobile phone or credit card.
The new regulations will be phased in over two years to allow companies to revise their practices.
The manufacture of CFC’s has been effectively phased out since their effects on the Ozone Layer became widely known.