A smoke screen is a dense cloud of fake smoke used to hide military areas.
$\mathrm{Ca}_3 \mathrm{P}_2+6 \mathrm{H}_2 \mathrm{O} \rightarrow 3 \mathrm{Ca}(\mathrm{OH})_2+2 \mathrm{PH}_3$
$\mathrm{PH}_3$ spontaneously catches fire to produce $\mathrm{P}_2 \mathrm{O}_5$ :
$2 \mathrm{PH}_3+4 \mathrm{O}_2 \rightarrow \mathrm{P}_2 \mathrm{O}_5+3 \mathrm{H}_2 \mathrm{O}$
$\mathrm{P}_2 \mathrm{O}_5$ forms a white dense smoke screen.