Part of the binding-protein-dependent transport system for phosphate; probably responsible for the translocation of the substrate across the membrane. The complex is composed of two ATP-binding proteins (PstB), two transmembrane proteins (PstC and PstA) and a solute-binding protein (PstS). 4-fold by phosphate starvation, part of the pstS3-pstC2-pstA1 operon. Belongs to the binding-protein-dependent transport system permease family. CysTW subfamily.