The hybridization is ${\mathrm{sp}}^3\mathrm{d}$ hybridization and phosphorous atom forms five ${\mathrm{sp}}^3\mathrm{d}$ hybrid orbitals. Five hybrid orbitals will be used to form bonds with five fluorine atoms. There are $5$ sigma bonds in this compound.

${\mathrm{PF}}_5\Rightarrow {\mathrm{sp}}^3\mathrm{d}$ hybridisation

($5$ sigma bonds, zero lone pair on central atom) Value of $\mathrm{y}=1$