Jax Blocking Autos

First of all this isn't a rant about how much I hate this ability. It is unique and I actually quite enjoy playing with him, one of my favorite older champions. I actually would like to ask the reasoning behind what kind of autos he blocks.

Today in a Poro King game, I noticed he doesn't block Ekko's Phase Dive, yet he is able to block almost every other charged auto attack along with Teemo's poison I am pretty sure (feel free to correct me on that if I am wrong and tell me if there are other charged auto attacks he can't block). I would just like some reasoning behind which autos can and cant be blocked, and not just "because Rito." Thank you for any clarity that can be provided.