Why are all P-Cl bond lengths equal in PCl3 but different in PCl5?

Phosphorus atom of PCl3, is sp3 hybridised. so orbital involved in hybridization are s and p only and PCl3 has a trigonal pyramid structure.

However in case of PCl5, the hybridisation is sp3d. (sp3d, the hybridisation can represent as also sp2+pd) and it acquired TBP ( trigonal pyramidal structure).
We know that in TBP, there is two type of bond present I.e. axial (longitudinal) and equatorial bond. Bond length of axial bond is longer (coordinate bond ) while equatorial bond is shorter due to covalent nature ( formed by overlapping of atomic orbitals).