An arrangement in which employees who are joining or leaving an organisation move from a part-time position into a full-time position or vice versa. In some cases, employees are given the flexibility to determine how many hours and when they work to ease their transition into/out of a full-time position.
Phasing in would include employees returning to work after an extended period of leave, e.g. on a part-time basis after maternity leave, caring for sick parents, etc., before converting back to a full-time position. Phased retirement is one example of Phasing out.