  We explore the impact of strain on charge carrier mobility of monolayer
$\alpha$, $\beta$, $\gamma$ and $\delta$-P, the four well known atomically thin
allotropes of phosphorus, using density functional theory. Owing to the highly
anisotropic band dispersion, the charge carrier mobility of the pristine
allotropes is significantly higher (more than 5 times in some cases) in one of
the principal directions (zigzag or armchair) as compared to the other.
Uniaxial strain (upto 6% compressive/tensile) leads to bandgap alteration in
each of the allotropes, especially a direct to indirect bandgap semiconductor
transition in $\gamma$-P and a complete closure of the bandgap in $\gamma$ and
$\delta$-P. We find that the charge carrier mobility is enhanced typically by a
factor of $\approx 5-10$ in all the allotropes due to uniaxial strain; notably
among them a $\approx 250$ (30) times increase of the hole (electron) mobility
along the armchair (zigzag) direction is observed in $\beta$-P ($\gamma$-P)
under a compressive strain, acting in the armchair direction. Interestingly,
the preferred electronic conduction direction can also be changed in case of
$\alpha$ and $\gamma$-P, by applying strain.
