Phantom assemblies are assemblies that have their own product structure, but whose assembly does not actually physically exist. The components of the phantom assembly are incorporated directly in the superordinate product. The product structure of the superordinate product contains a reference to the phantom assembly. You can use phantom assemblies for the following purposes:
To simplify the structure of bills of material: Phantom assemblies allow you to group components that belong together logically or functionally, without creating an additional level in the product structure. This can make the product structure easier to maintain and understand.
To reduce the number of material masters: Phantom assemblies do not require a material master record in SAP S/4HANA, as they are not physically produced or stored. This can save storage space and reduce the effort of creating and updating material masters.
To reduce the number of changes required in bills of material: Phantom assemblies can be used to represent common subassemblies that are used in multiple products. This way, you only need to maintain the product structure of the phantom assembly once, and any changes will be reflected in all the products that reference it.
Phantom assemblies do not increase the number of planning levels, as they are not considered as separate planning objects. They also do not make the assignment of components easier, as the components are assigned to the superordinate product, not to the phantom assembly. Reference: Phantom Assembly | SAP Help Portal, Phantom Assembly | SAP Help Portal, Planning Phantom Assemblies | SAP Help Portal.