MySQL query issue with Flex, php

I'm trying to pass a MySQL query with variables from flex to MySQL using php.

This is the Query in Flex. Everything appears to be correct.

mysqlQuery("INSERT INTO poc_note_test (first_name,last_name) VALUES ("+firstName+"," +lastName+")");

When the query is passed to my server via http to be processed by PHP it returns the following error

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'Test_Value )' at line 1

From what I can see it is trying to include the final ")" as part of the value. I for the life of me cannot see how to stop this from happening.

Here is the php that is being used to process the query where it errors out.

$sql = $_REQUEST['sql'];
$result = mysql_query($sql);
$err = mysql_error();
$cols_count = mysql_num_fields($result) or error_log('Invalid query: ' .mysql_error());

Any help will be much appreciated

This is the function passing the query. Maybe the issue is here?

public function mysqlQuery(sql:String,fid:String):void {

var http:HTTPService = new HTTPService;
var parm:Object = new Object;
parm.sql = sql;
parm.private_key = private_key;
parm.fas_db = mysql_db; 
http.url = mysql_url+"?irand="+Math.random();

http.showBusyCursor = true;
http.request = sql;
http.addEventListener(ResultEvent.RESULT, mysqlResult);
http.addEventListener(FaultEvent.FAULT, mysqlFault);
http.method = "POST";

sqlToken = http.send(parm);
sqlToken.param = fid;

}