You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4'S)-4'-butan-2-yl-2-phenoxyspiro[1,3,2lambda5-benzodioxaphosphole-2,2'-1-oxa-3-aza-2lambda5-phosphacyclopentane]-5'-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H20NO5P
assistant