Final answer:
The phylum that has triploblastic organisms with an incomplete digestive tract is Platyhelminthes, which includes flatworms.
Step-by-step explanation:
The phylum that has both three germ layers and an incomplete digestive tract is the Platyhelminthes. This group includes the flatworms which are triploblastic, meaning they develop from three embryological germ layers: the ectoderm, mesoderm, and endoderm. These layers give rise to the animal's tissues and organs during development. Flatworms are acoelomates because their bodies do not contain cavities between the outer surface and the inner digestive tract, and instead, the space is completely filled with tissue.
Moreover, many flatworm species have an incomplete digestive system, lacking an anus, with a single opening serving as both mouth and exit. This differentiated them from other triploblasts like mollusks, which typically have a complete digestive tract.