  Phosphorus related species are not known to be as omnipresent in space as
hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers
spotted very few P-bearing molecules in the interstellar medium and
circumstellar envelopes. Limited discovery of the P-bearing species imposes
severe constraints in modeling the P-chemistry. In this paper, we carry out
extensive chemical models to follow the fate of P-bearing species in diffuse
clouds, photon-dominated or photodissociation regions (PDRs), and hot
cores/corinos. We notice a curious correlation between the abundances of PO and
PN and atomic nitrogen. Since N atoms are comparatively abundant in diffuse
clouds and PDRs than in the hot core/corino region, PO/PN reflects < 1 in
diffuse clouds, << 1 in PDRs, and > 1 in the late warm-up evolutionary phase of
the hot core/corino regions. During the end of the post-warm-up phase, we
obtain PO/PN > 1 for hot core and < 1 for its low mass analog. We employ a
radiative transfer model to investigate the transitions of some of the
P-bearing species in diffuse cloud and hot core regions and estimate the line
profiles. Our study estimates the required integration time to observe these
transitions with ground-based and space-based telescopes. We also carry out
quantum chemical computation of the infrared features of PH3 along with various
impurities. We notice that SO2 overlaps with the PH3 bending-scissoring modes
around ~ (1000 - 1100) cm-1. We also find that the presence of CO2 can strongly
influence the intensity of the stretching modes around ~ 2400 cm-1 of PH3 .
