You shouldn't be using mysql
in 5.5. It is deprecated.
Deprecation of mysql_ functions
PHP functions that start with
mysql_
have been deprecated as of PHP 5.5.0. If you are in a position to do so, please consider updating your code to use the MySQLi or PDO extensions instead.
Anyway, use mysqli (which you seem to have in your question tags)
The phpinfo key is: $phpinfo['mysqli']['Client API header version']
rather than $phpinfo['mysql']['Client API version']
.