PHP联系表格问题

I'm having problems with this code. After submitting the filled form the display message (Email sent!) is not displaying next to the submit button. I need to display the Email sent message next to the submit button on the contact form. After submitting the form, I also need to clear the form fields even after a refresh or a back action. Kindly help me out with this code

Form Action Images:

Before Submitting the Form

After Submitting the form

<?php

$action=$_REQUEST['action'];

if ($action=="")    /* display the contact form */
    {
    ?>

    <form name="contactform" method="post" enctype="multipart/form-data">

        <input type="hidden" name="action" value="submit">

      <label for="your_name">Your Name <font color="red">*</font></label>
      <input  type="text" id="reset" name="your_name"  placeholder="Enter Your Name" maxlength="20" size="40" >

      <label for="email">Email Address <font color="red">*</font></label>
      <input  type="email" id="reset" name="email" placeholder=" Enter Your E-mail Address" maxlength="20" size="40" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,3}$" required>

      <label for="mobile_number">Mobile Number</label>
      <input  type="tel" id="reset" name="mobile_number" pattern="[0-9]{1}[0-9]{9}" placeholder="Enter Your Phone Number by Adding Country Code (eg: +91.,)" maxlength="30" size="40" >

      <label for="message">Message <font color="red">*</font></label>
      <textarea  name="message" id="reset" placeholder="Your Message Goes Here" maxlength="1000" cols="62" rows="10" required></textarea>

        <input type="submit" value="Submit">
        </form>



<?php
    }

else                /* send the submitted data */

    {

$your_name = $_REQUEST['your_name'];

$email = $_REQUEST['email'];

$mobile_number = $_REQUEST['mobile_number'];

$message = $_REQUEST['message'];

$formcontent="From: $your_name 
 Email: $email 
 Phone Number: $mobile_number 
 Message: $message";

$recipient = "name@email.com";

$subject = "Contact Form";

$mailheader = "From: $email 
";

    if (($your_name=="")||($email=="")||($message==""))
        {
        echo "All fields are required, please fill <a href=\"\">the form</a> again.";
        }
    else{       
        @mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");

        echo "Email sent!";
        }
    }  
?>

You can redirect the page after sent email or also can set a variable like $msg='email sent'; and call this variable before your submit button.

    $action=$_REQUEST['action'];

    if ($action!="")    /* display the contact form */
        {
$your_name = $_REQUEST['your_name'];

    $email = $_REQUEST['email'];

    $mobile_number = $_REQUEST['mobile_number'];

    $message = $_REQUEST['message'];

    $formcontent="From: $your_name 
 Email: $email 
 Phone Number: $mobile_number 
 Message: $message";

    $recipient = "name@email.com";

    $subject = "Contact Form";

    $mailheader = "From: $email 
";

        if (($your_name=="")||($email=="")||($message==""))
            {
            header('location: yoururl?msg=error');
            //$msg   =  "All fields are required, please fill <a href=\"\">the form</a> again.";
            }
        else{       
            @mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");

            header('location: yoururl?msg=succss');
            //$msg   =  'Email Sent!';
            }
        }
        ?>

        <form name="contactform" method="post" enctype="multipart/form-data">

            <input type="hidden" name="action" value="submit">

          <label for="your_name">Your Name <font color="red">*</font></label>
          <input  type="text" id="reset" name="your_name"  placeholder="Enter Your Name" maxlength="20" size="40" >

          <label for="email">Email Address <font color="red">*</font></label>
          <input  type="email" id="reset" name="email" placeholder=" Enter Your E-mail Address" maxlength="20" size="40" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,3}$" required>

          <label for="mobile_number">Mobile Number</label>
          <input  type="tel" id="reset" name="mobile_number" pattern="[0-9]{1}[0-9]{9}" placeholder="Enter Your Phone Number by Adding Country Code (eg: +91.,)" maxlength="30" size="40" >

          <label for="message">Message <font color="red">*</font></label>
          <textarea  name="message" id="reset" placeholder="Your Message Goes Here" maxlength="1000" cols="62" rows="10" required></textarea>
    <?php if(isset($_REQUEST['msg']) and $_REQUEST['msg']=='success'){echo "Email sent!";}if(isset($_REQUEST['msg']) and $_REQUEST['msg']=='error'){echo "All fields are required, please fill <a href=\"\">the form</a> again.";} ?>
            <?php echo $msg; ?>
            <input type="submit" value="Submit">
            </form>

Your code should be like this. Notice isset($_POST['submit'], $msg , value="".

<?php

    if(isset($_POST['submit']))
    {

    $your_name = $_REQUEST['your_name'];

    $email = $_REQUEST['email'];

    $mobile_number = $_REQUEST['mobile_number'];

    $message = $_REQUEST['message'];

    $formcontent="From: $your_name 
 Email: $email 
 Phone Number: $mobile_number 
 Message: $message";

    $recipient = "name@email.com";

    $subject = "Contact Form";

    $mailheader = "From: $email 
";

        if (($your_name=="")||($email=="")||($message==""))
            {
            $msg = "All fields are required";
            }
        else{       
            @mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");

            $msg = "Email Sent";
            }
        }  
    ?>

        <form name="contactform" method="post" enctype="multipart/form-data">

            <input type="hidden" name="action" value="submit">

          <label for="your_name">Your Name <font color="red">*</font></label>
          <input  type="text" id="reset" name="your_name"  placeholder="Enter Your Name" maxlength="20" size="40" value="">

          <label for="email">Email Address <font color="red">*</font></label>
          <input  type="email" id="reset" name="email" placeholder=" Enter Your E-mail Address" maxlength="20" size="40" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,3}$" required value="">

          <label for="mobile_number">Mobile Number</label>
          <input  type="tel" id="reset" name="mobile_number" pattern="[0-9]{1}[0-9]{9}" placeholder="Enter Your Phone Number by Adding Country Code (eg: +91.,)" maxlength="30" size="40" value="">

          <label for="message">Message <font color="red">*</font></label>
          <textarea  name="message" id="reset" placeholder="Your Message Goes Here" maxlength="1000" cols="62" rows="10" required></textarea>

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

          <?php echo $msg; ?>
            </form>