Ok this is very experimental but you might have a very slim chance if you try the following.
Search for the exact same file, it must have the same SHA1 of the lost incomplete file to work. Unfortunately you cant check what the lost SHA1 was...
Download a few KB of this file and let it collect candidates.

Now open your phexdownload.xml and change the incomplete-file-name tag like Manifest0 mentioned to point to your lost incomplete file.
Now look for tags that looks like this:
<finished-scopes start="0" end="5970"/>
<finished-scopes start="8359" end="597875"/>
Remove all finished-scopes tags except one and change it to look like this
<unverified-scopes start="0" end="900000"/>
Set the end value to about 10-20MB less then the file size you like to download.

What this hopefully does is that you mark almost the whole file as already downloaded but not verified. Phex will hopefully find a candidate providing a THEX tree of the file while downloading the missing 20MB. Once it has the THEX tree it will verify the whole file and... hopefully... throw away everything you have not successfully downloaded before.

But when you found a file with a different SHA1 Phex will very likely throw away everything you have downloaded before.. So its very important to find the exact same file...

Gregor

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