What is mean by Phantom Part
phantom parts are created because a business need, the majority of the phantom parts are assemblies used to facilitate some process step like planning, purchasing, assembling or any other specific reason that a particular business have. I agree with you that, in general, fastenings and piping elements are purchased parts in business those use these parts, not manufacturer them.
I`d suggest you to ask for the reason, probably it`s a business specific need or procedure.
Phantoms are parts that will never exist in physical form. As Carlos mentioned, they are often used for planning and purchasing, but not for manufacturing. An example is a placeholder assembly to drive MRP for long lead time components that is swapped with an actual assembly once the real assembly configuration is complete. I can’t think of a good reason why purchased components would be considered a phantom, so I would definitely question that practice.