In the isoquinoline ring system of the title mol-ecule, C(22)H(20)N(2)O(5), the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-aza-spiro ring is essentially planar [maximum deviation = 0.026 (1) Å] and forms dihedral angles of 22.53 (5) and 64.46 (5)° with the benzene and phenyl rings, respectively. The mol-ecular structure is stabilized by a weak intra-molecular C-H⋯O hydrogen bond, which generates an S(7) ring motif. In the crystal, mol-ecules are linked via weak inter-molecular C-H⋯O and C-H⋯N hydrogen bonds into layers parallel to (102).