  The astrochemistry of the important biogenic element phosphorus (P) is still
poorly understood, but observational evidence indicates that P-bearing
molecules are likely associated with shocks. We study P-bearing molecules, as
well as some shock tracers, towards one of the chemically richest hot molecular
core, G31.41+0.31, in the framework of the project "G31.41+0.31 Unbiased ALMA
sPectral Observational Survey" (GUAPOS), observed with the Atacama Large
Millimeter Array (ALMA). We have observed the molecules PN, PO, SO, SO2, SiO,
and SiS, through their rotational lines in the spectral range 84.05-115.91 GHz,
covered by the GUAPOS project. PN is clearly detected while PO is tentatively
detected. The PN emission arises from two regions southwest of the hot core
peak, "1" and "2", and is undetected or tentatively detected towards the hot
core peak. the PN and SiO lines are very similar both in spatial emission
morphology and spectral shape. Region "1" is in part overlapping with the hot
core and it is warmer than region "2", which is well separated from the hot
core and located along the outflows identified in previous studies. The column
density ratio SiO/PN remains constant in regions "1" and "2", while SO/PN,
SiS/PN, and SO2/PN decrease by about an order of magnitude from region "1" to
region "2", indicating that SiO and PN have a common origin even in regions
with different physical conditions. Our study firmly confirms previous
observational evidence that PN emission is tightly associated with SiO and it
is likely a product of shock-chemistry, as the lack of a clear detection of PN
towards the hot-core allows to rule out relevant formation pathways in hot gas.
We propose the PN emitting region "2" as a new astrophysical laboratory for
shock-chemistry studies
