What is Phase ?
Phase is (noun) a stage in the development of something The project is now in its final phase. It’s a phase she’s going through and hopefully she will grow out of it. I’m sure dyeing his hair green is just a phase. (verb) to phase something in, to phase something out to introduce or to remove something gradually The new telephone system will be phased in over the next two months.
source: Easier English, Student Dictionary Upper Intermediate Level