<?php
$array = array(
   "1" => "android",
   "2" => "apple",
   "3" => " iphone 6",
   "4" => " iphone 5",
   "5" => " iphone",
   "6" => "blackberry",);

$phone=[];
foreach($array as $value){
if(substr($value, 0, 1)==' '){
$apple=(end($phone));
$string=[$apple=$apple.$value];
}else{
$phone[]=$value;
}}
?>

var_dump ($apple=$apple.$value);