An IOP is similar to a PHP, but it lasts only three hours a day for a minimum of four days a week (again, subject to your state laws and insurance requirements, this may differ slightly in your area).
In an IOP for OCD, most of the group work not specifically focused on OCD is eliminated, and the focus is mainly on doing ERP and CBT. During an IOP, you may be working on your exposures at the hospital or clinic, or you may even leave the building to work with your therapist in the environment where you experience your fear.
For example, if you perform rituals surrounding checking the locks on your car doors, you and your therapist may go out to the parking lot and actually have you lock the doors once and then walk away from the car without going back to check and make sure that they are locked.
IOP programs are a good step-down from a PHP program and are also useful if a person requires more intensive therapy than can be provided in a traditional outpatient therapy (typically once-a-week therapy appointments) setting, but does not need the intensity of a PHP.
Psychiatrists are still able to consult with their patients while they are in an IOP level of care.