The phyla that lack organs are the Porifera (sponges). They are asymmetrical, meaning they do not have a defined body plan with symmetry.

Here's why:

* Porifera: Sponges are the simplest multicellular animals. They lack true tissues and organs. Instead, they have specialized cells that perform various functions. Their body is a loose aggregation of cells that filter water for food and oxygen.

* Asymmetry: This means that a sponge's body cannot be divided into two identical halves. They are irregular in shape and lack a definite head, tail, or body axis.

While other phyla like Cnidaria (jellyfish, corals) and Platyhelminthes (flatworms) have simpler body plans compared to higher organisms, they do have organs.