A 58-year-old man with Stage 4 CKD (eGFR 22 mL/min/1.73m²) due to diabetic nephropathy presents with fatigue and dyspnea on exertion for 3 months. His hemoglobin is 8.2 g/dL, MCV 78 fL, serum iron 45 µg/dL, ferritin 320 ng/mL, TSAT 18%, and reticulocyte count 0.8%. Serum creatinine is 3.8 mg/dL, phosphate 5.2 mg/dL, calcium 7.8 mg/dL, and PTH 385 pg/mL. He has not received any prior ESA therapy. What is the most appropriate next step in management?