PHI stands for Protected Health Information.
The HIPAA Privacy Rule provides federal protections for personal health information held by covered entities and gives patients an array of rights with respect to that information. At the same time, the Privacy Rule is balanced so that it permits the disclosure of personal health information needed for patient care and other important purposes.
Learn more about protected health information at: http://www.hhs.gov/ocr/privacy/hipaa/understanding/index.html