We study the evolution of phosphorous-bearing species in one-dimensional C-shock models .
We find that the abundances of P-bearing species depend sensitively on the elemental abundance of P in the gas phase and on the abundance of N atoms in the pre-shock gas .
The observed abundance of PN and the non-detection of PO towards L1157 B1 are reproduced in C-shock models with shock velocity v = 20 km s ^ { -1 } and pre-shock density n ( H _ { 2 } ) = 10 ^ { 4 } -10 ^ { 5 } cm ^ { -3 } , if the elemental abundance of P in the gas phase is \sim 10 ^ { -9 } and the N-atom abundance is n ( N ) / n _ { { H } } \sim 10 ^ { -5 } in the pre-shock gas .
We also find that P-chemistry is sensitive to O- and N-chemistry , because N atoms are destroyed mainly by OH and NO .
We identify the reactions of O-bearing and N-bearing species that significantly affect P chemistry .