Often the file you like to download is available on different hosts. Phex will request different segment of the file from each host in parallel. After successfully downloading a segment Phex will merge it with the other segments of the file. This results in a much higher download speed. If a host is too slow the segment is split during download and given to an another host. To make sure you never run out of hosts Phex is able to find new download hosts by itself with the automatic search functionality.