Erase iPhone without a computer

You will need a computer to erase and restore an iPhone. Perhaps you have a friend who could help. If not, make an appointment at the nearest Apple store for assistance.

Apple Store - Find a Store - Apple

How to erase your iPhone, iPad, or iPod touch - Apple Support

Note that he only asked about erasing the phone without a computer, he did not ask about restoring it.

I see that I read too much into the question! Sorry!