<?php
$string = "
Name: John Doe
Address: 123 Main St
City: Chicago
State: IL
Zip: 60021
Name: Jane Smith
Address: 123 State Ave
City: Boston
State: MA
Zip: 02501
Name: John Doe
Address: 123 Main St
City: Chicago
State: IL
Zip: 60021";
preg_match_all('!(Name.*|Address.*|City.*|State.*|Zip.*)!', $string, $results);
$records = array_chunk($results[0], 5);
var_dump($records);