A novel and transition metal-free synthesis of benzo-δ-phosphonolactams from readily available ethyl arylmethylphosphonochloridates and dibenzo[b,f][1,4]oxazepines was developed. The reaction includes tandem phosphonylation, deprotonation, intramolecular nucleophilic addition, and aromatization, affording various polycyclic benzo-δ-phosphonolactams in moderate to good yields and diasteroselectivity in one-pot (up to 96% yield and 83 : 17 dr).