A 15-year-old girl with history of anorexia nervosa presents to the ED after a syncopal event at home. She is brought in by her parents who say she has been limiting her food portions and has increased her physical activity in recent weeks. She is bradycardic in the ED and orthostatic vitals are abnormal. Her labs show a low normal glucose, mildly decreased potassium, and significant depletion of phosphate. You plan on admitting the patient. Which of the following would be acceptable treatment in the ED?