What metamorphic rock that has regional metamorphism has the highest grade of metamorphism?  GneissPhyllite

Gneiss has the highest grade of metamorphism in regional metamorphism. This means it has been subjected to the highest temperatures and pressures compared to other metamorphic rocks. The process of formation involves intense heat and pressure causing profound physical and/or chemical change. The minerals in the original rock, or protolith, recrystallize into larger sizes and the rock becomes denser. The rock also develops a pronounced foliation, or banding, due to the alignment of minerals.