Nominal transmission and distribution voltages are line voltages. So '66 kV' is a line-to-line voltage. Note that there is no such thing as a 'phase-to-phase' voltage -the correct term is 'line-to-line'. Using the term, 'phase-to-phase', indicates a lack of understanding of a.c., which is not uncommon! Incidentally, the symbol is 'kV', not 'KV'.