The PMHNP on an inpatient substance disorder unit is reviewing the labs for a 17-year-old patient diagnosed with anorexia nervosa who was recently introduced to a caloric intake program. She has pain on eating, and her labs are as follows: phosphorus 0.7 mg/dL, potassium 1.4 mEq/L, and magnesium 1.8 mg/dL. Which of the following is this patient most at risk for?