PHP Parse error: syntax error, unexpected $end in my file

You should add double quote in place of single quote. If you want to add single quote then add ''.

$writer->writeElement("FirstName","");

Double quote will not generate any error.So remove single quote and add double quote.

Error in this line

$writer->writeElement('FirstName',");

You can give two double quotes as

$writer->writeElement('FirstName',"");

or Two single quotes as

$writer->writeElement('FirstName','');

You haven't closed the double quotation at this line

$writer->writeElement('FirstName',");

You may use this instead

<?php
// File: gs_phonebook.php
// version: 1.0
// Description: Generating a XML Phonebook from FreePBX MySQL DB
//!!Enable for Debug only!!
error_reporting(E_ALL);
ini_set("display_errors",ON);

// Database settings
$DBhost="comms.****";
$DBuser="****";
$DBpass="****";
$DBdatabase="asterisk";

// Connect to the Database and get all devices
$DBlink=mysql_connect($DBhost,$DBuser,$DBpass) or die("Could not connect to host.");
mysql_select_db($DBdatabase,$DBlink) or die("Could not find database.");
$DBquery="SELECT user,description FROM devices ORDER BY descriptionASC";
$QUERYresult=mysql_query($DBquery,$DBlink) or die("Data not found.");

//Setup XMLWriter
$writer =newXMLWriter();
$writer->openURI('/tftpboot/gs_phonebook.xml');
$writer->setIndent(4);

//Beginn output
$writer->startDocument('1.0');
$writer->startElement('AddressBook');

//Add extensions / contacts from devices to the xml phonebook
while($contact=mysql_fetch_array($QUERYresult)){
$writer->startElement('Contact');
$writer->writeElement('LastName',$contact['description']);
$writer->writeElement('FirstName',"");
$writer->startElement('Phone');
$writer->writeElement('phonenumber',$contact[user]);
$writer->writeElement('accountindex','0');
$writer->endElement();
$writer->endElement();
}

$writer->endElement();
$writer->endDocument();$writer->flush();
?>

As the code highlighting shows, on this line:

$writer->writeElement('FirstName',");

You have a mismatched double quote- you need '' instead of " (or something instead of ")

$writer->writeElement('FirstName',");

That looks like a double quote rather than 2 single quotes. You can tell from the messed up colouring on the SO codeblock.

Should be like this:

$writer->writeElement('FirstName','');