<?php
$str = "Text containing \n082/5/2016\n0825/2016\n08/252/016\n08/25/201\n0/85/2016\n08/25/2016";
$result = preg_replace('~\b(?=(?:\D*\d){7,8})\d+(?:/\d+)+\b~', "", $str); echo $result;
PD9waHAKCiRzdHIgPSAiVGV4dCBjb250YWluaW5nIFxuMDgyLzUvMjAxNlxuMDgyNS8yMDE2XG4wOC8yNTIvMDE2XG4wOC8yNS8yMDFcbjAvODUvMjAxNlxuMDgvMjUvMjAxNiI7IAokcmVzdWx0ID0gcHJlZ19yZXBsYWNlKCd+XGIoPz0oPzpcRCpcZCl7Nyw4fSlcZCsoPzovXGQrKStcYn4nLCAiIiwgJHN0cik7CmVjaG8gJHJlc3VsdDs=