Sure,
Right now, you do light validation and filtering on all compulsary fields. For example, you have:
$camp_code = trim($_POST['camp_code']);
In the process of trimming the posted value, you are assigning it to $camp_code.
However, your optional fields don't get assigned anywhere (that I can see). At the very least you should have a line like:
$fax_number=$_POST['fax_number'];
Before $fax_number is used in the email text.
As I said, this would be the bare minimum for functionality. Leaving values unfiltered, especially when they'll be included in an email, is asking for trouble. But that's a separate issue .