Here is a good tutorial on php and web forms:
http://www.w3schools.com/php/php_forms.asp
Read the above brief tutorial and then follow below...
As for adding them into the body of the email phMailer sends,
you will want to find the line:
$message.="$yourmessage";
Basically, create a new line two lines above it and replace $yourmessage with your $_POST information.
An example would look like:
$message.="Company Name: $_POST['company_name']";
$message.="\n";
$message.="Another field: $_POST['field_name']";
$message.="\n";
$message.="$yourmessage";
Sorry if this is a bad explanation, im not to good at explaining things.