Why it is not phylum or it can be order as it contains species, genus and family?
Each taxonomic rank is more specific than the one before it. For example, the phylum Chordata includes everything from a sea squirt to a human. Order on the other hand would be more speicific, for example the order Primate. This includes us humans and other animals like lemurs, chimps, and gorillas, but excludes almost all of the other animals that the phylum Chordata included. Therefore, you can't interchange phylum and order, but phylum contains order. Order does NOT contain phylum.
I don't completely understand your question, but hopefully that helped.