PHP constant encapsed string php error

This is the error I am getting.
"Parse error: syntax error, unexpected T_CONSTANT_ENCAPSED_STRING in on line 188"
What I am trying to do is connect to the database and insert data into the table, but i can't figure out this error.

$tableName = "customer";
$nullStr = "NULL";

$SQLstring = "INSERT INTO $tableName VALUES
            ('".$nullstr."','".$fname."', '".$lname."','".$address."','".$state."','".$zip."',          '".$phone"','".$email"')";
$result = $mysqli->query($SQLstring);