Go to inventory part, zoom in on Part Status column. Once you are in the basic data, if there isn’t any, create a new part status for P - Phase Out. Set it as supplies not allowed, but allow on hand and demands. Update your inventory parts with this part status - which will allow to consume parts, but not create any supplies like purchase reqs.

To use up the existing stock of a component before starting to buy the new one you can you alternate component functionality.

Create a new revision of the BOM containing the new component. Then setup the old component as an alternate to the new component and select to allow MRP netting. Then also select to consider alternate components when running MRP. Now MRP will only create PR for the new component once all stock of all component has been used up.

SOR created with expected usage of an alternate component are indicated with a check box so the planner can remember to replace the new to the old component for relevant Shop Orders.