Phenoxybenzamine HCl is primarily used in the management of pheochromocytoma, a rare tumor of the adrenal gland that causes excessive release of adrenaline and noradrenaline. It works by blocking alpha-adrenergic receptors, which helps to control high blood pressure and prevent hypertensive crises during surgery or other stressful events. This medication is also employed in the treatment of certain cases of Raynaud's disease and other conditions involving excessive vasoconstriction. Additionally, it is sometimes used off-label to manage symptoms of benign prostatic hyperplasia (BPH) by relaxing the smooth muscles in the prostate and bladder neck, improving urine flow. Due to its long-lasting effects, it is particularly useful in preoperative preparation for patients with pheochromocytoma to stabilize blood pressure and reduce the risk of complications.