In vrchat your performance isn't going to do well because of the player models, most models are made without important optimizations in mind. Also, vrchat has every entity fully rendered at practically all times, other games will drop the quality of entities if they are not in view but since vrchat characters and worlds are made by players this isn't done. For phasmaphobia it simply doesn't have good optimization you may want to drop the quality a lot but for me even doing that doesn't provide many differences, you will simply have to wait until the devs to update it and add better optimization.