Issue

The phase block spell makes targeted blocks disappear for a specific amount of time, this facet works as intended. However, an affected block's density is not modified, impassible blocks remain impassible.

Recreating

:)

Testing & Proof

I'm not having this issue either in dev or in a small test instance. Plausibly some other mod you're using is breaking it? Can you figure out the minimal set of mods which reproduces this bug and let me know?

This seems to only be an issue when using Lithium: https://www.curseforge.com/minecraft/mc-mods/lithium
Can confirm with just Hexal and Lithium installed.

... huh
is it also an issue with Lithium and Yttr's Void Effector (or however you spell it)?