PHP动作/ salesForce

I have been asked to update a contact form, i always leave action blank(action="") in any forms i have worked on before. I have been sent the following form as seen below. When the form is submitted, it is sent to the url, which is a blank screen. Has anyone implemented a salesForce contact form before ?

<form action="https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8" method="POST">

  <input type=hidden name="oid" value="00D200000005wgb">
  <input type=hidden name="retURL" value="http://"> <!--  add URL of completed page here    

-->

   <label for="first_name">First Name</label><input  id="first_name" maxlength="40" name="first_name" size="20" type="text" /><br>

   <label for="last_name">Last Name</label><input  id="last_name" maxlength="80" name="last_name" size="20" type="text" /><br>

   <label for="email">Email Address</label><input  id="email" maxlength="80" name="email" size="20" type="text" /><br>

   <label for="phone">Phone</label><input  id="phone" maxlength="40" name="phone" size="20" type="text" /><br>

     <select id="country" name="country" title="country">
       <option value="London">London</option>
       <option value="Midlands">Midlands</option>
       <option value="North England">North England</option>
       <option value="South England">South England</option>
       <option value="Wales">Wales</option>
       <option value="Scotland">Scotland</option>
       <option value="Northern Ireland">Northern Ireland</option>
     </select><br>


     <textarea id="00N200000016Kk5" name="00N200000016Kk5" rows="4" type="text" wrap="soft"></textarea><br>

      <!-- Below 3 fields are hidden  -->
      <select id="recordType" name="recordType" style="display:none;">
        <option value="012w0000000QCbe">Prospect UK</option></select>
        <select id="00N20000001L8Pi" name="00N20000001L8Pi" title="Web Source" style="display:none;"><option value="Download Whitepapers UK">Download Whitepapers UK</option>    </select>  
      <select id="lead_source" name="lead_source" style="display:none;">
      <option value="Download Whitepapers UK">Download Whitepapers UK</option></select>


      <input type="submit" name="submit">

   </form>

The action attribute of a <form> is basically a redirect for the form that sends the POST or GET data along with it.

1. If action is left blank, it redirects to the current URL, thus "refreshes".
2. If action is a link beginning with http:// or https://, the form sends the $_POST / $_GET request to the full page link.
3. If action is set to a link not beginning with http:// nor https://, the link set in the action is added to the current sub-directory in the same way a php include works.

Therefore, this in your code:

<form action="https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8" method="POST">

Will send a POST request to https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8