The name is the variable used in the php section so all your fields in your form need a name.
<li><p>Telephone No </p><p><input type="text"></p></li>
<li><p>Telephone No </p><p><input type="text" name="telephone"></p></li>
The variable needs to be set on the php page and depending on the php version there are different options but I think this is the current method:
$telephone = $_POST['telephone'];
The variable $telephone now contains the value from the telephone field in your form.
Then in your email you need to add all these variables together and add to your email.
It may be worth your while finding a form and modifying it to your needs; this is one I have used in the past: