title: How best to validate a mobile phone number based on character length, starting with and numeric using php
body: <p>Hi I have a mobile phone number field.</p>
  
  <p>I am currently validating if empty:</p>
  
  <pre><code>&lt;?php
     if ($_REQUEST['text_message'] &amp;&amp; !@$_REQUEST['text_message_mobile']){
        $errors[] = "Please enter your mobile number for text messages";
     }
  ?&gt;
  </code></pre>
  
  <p>I would like to add validation to check that the mobile number is 11 characters long and begins with 07.</p>
  
  <p>An example accepted phone number would be 07123456789</p>
  
  <p>How best would I go about adding this validation using php?</p>
  
  <p>Thanks for any help :o)</p>