$re = '/class=([^=]*)([^(a-z|A-Z|0-9|\-|_)])btn("|([^(a-z|A-Z|0-9|\-|_)]).*")/';
$str = ' <a href="tel:{{ message.contact_phone }}" data-message-phone-btn class="bottom-bar__btn"><i class="mypro-icon mypro-icon-phone"></i><br>{{ _("Appeler") }}</a>
<a href="sms:{{ message.contact_phone }}&body={{ body|urlencode }}" data-message-sms-btn class="bottom-bar__btn hide-for-medium-up"><i class="mypro-icon mypro-icon-sms"></i><br>{{ _("SMS") }}</a>
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php