Phase in
Definition 1 of 1
Pro Tip 1/3Gradual Process
Think of 'phase in' as making slow, step-by-step changes rather than all at once. 
The school will phase in the new curriculum, starting with 9th grade next year.
Pro Tip 2/3Planned Stages
When something is 'phased in', it's often part of a planned strategy with clear stages. 
We'll phase in remote working, beginning with one day a week.
Pro Tip 3/3Common Contexts
'Phase in' is frequently used in contexts like business, government, and technology. 
The software update will be phased in for different user groups over the next month.