What you will need:
- The latest version of Red Flags
- 1 Wall Zombie
- 1 Thin Static Wall (with the other side of it being an open space about 1 body away)

Steps:

Step 1: Lean towards the static wall.
Step 2: Get the wall zombie to push you into the wall with its wall.
Step 3: Walk towards the static wall

Now you're at the other side of the wall. There we go, that's wall phasing. Started off as a bug, now it's a feature.