To keep up with security on the IBM i, your company will eventual support long passwords and more characters. This means people can use symbols and lower case characters which will help increase the difficulty of guessing a password. The problem you may run into with your PHP script is if you were using the strtoupper() function on your password and your username variable you’ll now have to remove that function because lower case symbols are now valid. You’ll also warn your users that the login page is now case senstive.
FYI: In V5R1, the i5 added support for long passwords and by default it was set to off. The QPWDLVL is what you need to change. You can set the max length of the password using QPWDMAXLEN. If you are using a custom login page you may need to rewrite it or switch to QSYS/QDSIGNON. You will have to IPL the system after this change