in 1.18.1 there is a problem that cause the phantom form to take damage when inside a blocks

Duplicate of #473

It's a current incompatibility with Lithium. Lithium has added a new rule for optimizing entity suffocation checks, which currently causes Phantom (and any other origins with phasing powers) to suffocate while moving through blocks.

To disable this new optimization rule, you can set the value of the mixin.entity.collisions.suffocation field inside the lithium.properties file from your Minecraft's (or server's) config folder to false, like so:

# This is the configuration file for Lithium.
# This file exists for debugging purposes and should not be configured otherwise.
#
# You can find information on editing this file and all the available options here:
# https://github.com/jellysquid3/lithium-fabric/wiki/Configuration-File
#
# By default, this file will be empty except for this notice.
mixin.entity.collisions.suffocation=false