Really cool! I had a nice time stacking objects, and the fact that it goes from small to big makes it even better. Also, I'm glad you locked in the pieces of the previous phase when you move to the next phase, because otherwise I'd never have made it to the end!
There was bug where it would sometimes move to the next phase before I actually made it to the arrow (think it happened when I dragged a piece too high, potentially?). Otherwise, like everyone else said, music would have made this even better. And, like you mention in the description, having randomised items to place would probably be better, since some items are just straight up better than others.
But yeah, overall, a great entry. Nicely done!