I think it has to do with state of mind, suspense, influences and tension.
Misery and Identity are psychological thrillers. Whereas a move like The Mist, Cube, Pet Semetary, Saw, The Conjuring, Don't Breathe, Paranormal Activity are psychological horror.
Horror is more for shock value and reaction, whereas thriller is dealing with mental conflicts and internal struggles within the character him/herself- The Woman in Black.
The traits of psychological thrillers tend to deal with phobias, obsessions, mental deficiencies, like The Honeymoon, The Crazies, 48 Meters Down..
Psychological horror is dealing with the surroundings and interactions with others along with the physical interactions.