You must always know what your Wi-Fi password is. Or how to retrieve it. iPhone imposes a limitation in terms of viewing saved passwords. So in order to find the Wi-Fi password on your iPhone, you will have to access the IP for your router.
Go to the Settings app and tap on Wi-Fi.
Select the icon next to your Wi-Fi network to view Wi-Fi information.
Scroll down to the DHCP tab and get the IP address listed for the Router.
Launch Safari on your iPhone, and type in the Router IP address. When prompted to log in, use the default user name (admin) and password (admin), unless you have changed this info.
Once logged in, go to the Wireless Settings and click on ‘Wireless Security’. Here you’ll find an entry ‘Security Key’. This is the password for your Wi-Fi. When you tap on the field the password will be revealed.