How can I show a block on a specific page if a custom PHP function evaluates to be true?
By enabling core PHP Filter module, you will see another option "Pages on which this PHP code returns TRUE (experts only)" under Show block on specific pages of the block configuration page. Select the option and write the following code in the box.

&lt;?php
  if (mymodule_is_iOS()) {
    if (arg(0) == 'node' &amp;&amp; arg(1) == 'add' &amp;&amp; arg(2) == 'profile-picture') {
      return TRUE;
    }
  }
  return FALSE;
?&gt;


Your module must have a lower weight than the core PHP filter module to allow this code snippet to call mymodule_is_iOS().