Just being on the cell phone does not violate HIPAA in and of itself. HIPAA has to do with disclosure of confidential health/medical information. If she is doing that, report her to HR as well as her lazy work ethic--the more co-workers complain, the more weight it will have.
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If you have already reported it to the manager, and the manager has not done anything about it, I am not sure what else you can do. What you describe does not appear to be a HIPAA violation. Try and ignore the co-worker.