$str = "old iccid : 809831 3245 345 new iccid : 999000 112221"

$output = "old iccid : 8098313245345 new iccid : 999000112221";

$output = preg_replace( '/d[ *]d/', '', $str);

$output = preg_replace('/(?<=d)s+(?=d)/', '', $str);