Phosphatase catalytic subunit of the trehalose synthase complex that catalyzes the production of trehalose from glucose-6-phosphate and UDP-alpha-D-glucose in a two step process. alpha,alpha-trehalose 6-phosphate + H2O = alpha,alpha-trehalose + phosphate Carbohydrate biosynthesis. Repressed by salt and thermal stress. In the C-terminal section; belongs to the trehalose phosphatase family. In the N-terminal section; belongs to the glycosyltransferase 20 family.