<?php
$mystring="PHPize.online is a free online environment for quickly running, experimenting with and sharing PHP and SQL code. You can run your SQL code on top of most popular RDBMS, and run PHP code that can use the same DB.";
$words = preg_split( "/( )/", $mystring );
$len=strlen($words);
$chunk=ceil($len/3);
$parts=str_split($words, $chunk);
print_r($parts);