Treatment plans are the full "plan of attack" for a patient’s treatment. It should list all treatment necessary for the patient.
Phases divide the treatment plans regarding sequencing. An example in an orthodontics office – perhaps treatment should be divided as early treatment (Phase 1), mid treatment (Phase 2), and late or finishing treatment (Phase 3).
Orders further sub-divide the phases. Perhaps before an orthodontist may band a patient’s teeth there is a need to extract one or more teeth. Therefore, Phase 1 could have the extraction as Order 1 and the banding as Order 2.