Atomic No. of Phosphorous is 15, so the electronic config. will be 2, 8, 5
to complete its Octate three more electrons are required, and in the same way,
Chlorines atomic no. is 17, so the elec. config would be 2, 8, 7
Here, Chlorine requires 1 electron to complete its octate, therefor chlorine will take electrons from the other element and phosphorous will also take three electrons from the other element. And this can be done by sharing of electrons and this kinda sharing is always happens in Non-Metals
So in PCl5 sharing of electrons will take place.