If it is a commercial insurance plan, Bill per the auth. You will need to get the residential treatment authorized. So that will be authorized in a date range. So you bill that date range with the auth, on a UB04. Then the patient should drop level of care to PHP, then IOP Or OP. PHP, IOP, and OP all get billed on Ub's if billing a facility/hospital or a HCFA if billing for a LISAC or other professional. So it depends on how your billing and who your listing as your providers.
Learn your levels of care. Detox, RTC, PHP, and IOP will almost always require pre-auth which will require utilization review.