Background: Phyllodes tumors (PTs) are rare fibroepithelial breast neoplasms spanning a benign-to-malignant spectrum, and the extent of surgery and reconstruction differs markedly by histologic grade. The primary aim of this study was to derive a grade-stratified surgical and reconstructive algorithm. Methods: The charts of patients diagnosed with phyllodes tumor at Kyungpook National University Chilgok Hospital between January 2011 and February 2026 were retrospectively reviewed. Tumors were classified by World Health Organization criteria as benign, borderline, or malignant, and the treatment protocols, extent of surgery, and immediate reconstruction after mastectomy were analyzed. Results: Of 417 patients charted, 401 were confirmed to have phyllodes tumors and 334 carried a definitive histologic grade. Together, they formed the analyzed cohort: 251 benign (75.1%), 55 borderline (16.5%), and 28 malignant (8.4%). Benign tumors were managed predominantly by breast-conserving surgery (BCS). Twenty-six patients formed the surgical cohort, defined by the reconstructive requirement of the resection defect: all total mastectomies (n = 19) together with all breast-conserving resections reconstructed by the plastic surgical team (oncoplastic breast-conserving surgery, n = 7). Reconstruction was performed in 21 (80.8%) with latissimus dorsi-based flaps, local flaps, or direct-to-implant reconstruction. Adjuvant radiotherapy was confined to malignant disease (7 of 15 malignant PTs, 46.7%; p = 0.010). Over a median follow-up of 32.7 months, local recurrence developed in four patients (15.4%) and two malignant tumors were fatal. In an illustrative case of recurrent malignant PT with rib metastasis, a widely opened pleural cavity was sealed with a single sheet of non-fenestrated acellular dermal matrix (ADM), which was found to be fully incorporated and still sealing the pleura at later implant explantation. Conclusions: A grade-stratified strategy (BCS for benign tumors and mastectomy with reconstruction for borderline/malignant disease) balances oncologic safety with aesthetic outcome.