The term that denotes the larger mineral grains in a porphyritic igneous rock is phenocrysts.

Here's why:

* Porphyritic texture is characterized by the presence of two distinct crystal sizes:

* Phenocrysts: These are the larger, well-formed crystals that grew first during the magma's cooling.

* Groundmass: This is the finer-grained matrix surrounding the phenocrysts, representing the later stage of cooling and crystallization.

So, while the rock itself is called porphyritic, the specific term for the larger grains within it is phenocrysts.