If PHP couldn't find a php.ini file at startup then phpinfo prints just one of the directories where it expects php.ini to be (without the filename itself).
If PHP could find a php.ini file at startup then phpinfo always print the full path to php.ini including the file.
But you can specify the path by setting the environment variable PHPRC to e.g. C:\PHP
So set PHPRC to C:\php then restart the web server and check in the phpinfo output if the directory changed.
Additionally, on Windows you can set a registry key (I think you don't need to do this if you set PHPRC, just make sure that the key has the correct value in case it already exists):
HKEY_LOCAL_MACHINE\SOFTWARE\PHP\5\IniFilePath -> c:\php