My last day at work so I have to give back my iPhone. How do I clear all the contact details without having to delete them one at a time?

Can you not just do a factory reset?

There is a reset option in the Settings app. You can also do a factory reset when it is connected to iTunes.

Settings > General > Reset

Thats what I did, I give my old one to the wife. Im not dead yet so I assume that works pretty well.

I did : Settings > General > Reset and Clear Contacts

the result was a phone that could only make emergency calls, had no apps, no internet, nothing.

I spent the rest of the train journey bored and then couldn’t ring the bloke i was meant to be meeting!