Again in /usr/local/lib/php.ini . Find the line with disable_functions. You probably have disable_function= with a long list of disabled functions, one of them likely being phpinfo. You'll need to remove phpinfo from the list of disabled functions in disabled_functions=
Alternatively within WHM go to PHP configuration Editor and Click Advanced and search for disabled functions
You'll find the phpinfo() in the text box. Just remove it and click save at the bottom.
This should also update the php.ini.
Yes, the previous posts are accurate. Look for "phpinfo" under disable_functions in /usr/local/lib/php.ini or with "Advanced Mode" via "WHM Home » Service Configuration » PHP Configuration Editor".