Version 3.7 will allow you to make it so that your users can enter their city when they register for your PHPFox based website, this article will show you how to do this.
Login to your admincp and select Settings > Manage Settings. On the Manage Settings screen click Registration under Global Settings.
On the Registration settings screen, scroll down to find the City in Registration option, select True from the dropdown, and then click Submit.
Your new members will now be given the option to enter their city when they register for your PHPFox based website!