Wyvern Tor Team #1: Willem, Krivath, Theirastra, Alecks
The wall appears to be there, though Willem might not know that he wouldn't be able to push his sword through an illusion due to the mental influence. A phantasm, yes. Illusion, no.
However, up close, it's clear that it is the backside of a secret door. There's a lever on the left side in the upright position, so it seems reasonable that if he pulls it down, it might release the mechanism holding the door in place.
When Theirastra approaches the wall while Willem was looking for the secret door, she, too, heard voices. Muffled as they were, she winds up only recognizing one of them... it sounds like Mithra.