I'm fine calling Backgammon 1.5-D. Physically you focus on a single dimension, and the second one matters too but it's not the same.
E.g. a pawn can move exactly 8 squares towards its opponents end (16 on its first move if no piece occupies 8 squares away), but can only capture 7 or 9 squares forward (with some extra modulo math to prevent wrapping)