Development Release Phase
A configured part in the Development release phase behaves like a part in Work-in-Progress (WIP) mode. The part is not used in production and can be modified with or without a change object attached to it.
Also, select Change Required if a change object is to be applied to the part. Under change-required, you can select whether the part is to be in the Development or Production release phase. Without change-required, you cannot assign the Production phase to the part while creating it (Development phase is required and set for you).