<?php
$email = "foo@bar.com";
$whatsapp = "";
$html = "<h1>Aqui começa seu HTML</h1>" .
(($email != "") ? "<strong>E-mail: {$email}</strong>" : "") .
(($whatsapp != "") ? "<strong>WhatsApp: {$whatsapp}</strong>" : "");
echo $html;
PD9waHAKCiRlbWFpbCA9ICJmb29AYmFyLmNvbSI7CiR3aGF0c2FwcCA9ICIiOwoKJGh0bWwgPSAiPGgxPkFxdWkgY29tZcOnYSBzZXUgSFRNTDwvaDE+IiAuCiAgICAgICAgKCgkZW1haWwgIT0gIiIpID8gIjxzdHJvbmc+RS1tYWlsOiB7JGVtYWlsfTwvc3Ryb25nPiIgOiAiIikgLgogICAgICAgICgoJHdoYXRzYXBwICE9ICIiKSA/ICI8c3Ryb25nPldoYXRzQXBwOiB7JHdoYXRzYXBwfTwvc3Ryb25nPiIgOiAiIik7CgplY2hvICRodG1sOw==