Just a portion of the pass phrase awould enable most cracking algorithms a 98% chance to succeed....
In the early days, PGP was open source. It was practically impossible for anyone to insert a back door; too many cryptologists and programmers would’ve seen it and raised the alarm. Now that Symantec owns it . . . who knows?
Oops, sorry, databoss. My last comment was meant for Loyal Sedition.
It won't help you at all with PGP providing you have a robust enough passphrase. I could give you 10 characters of my PGP passphrase, and you'd still need millenia to decrypt my stuff. That is, if what you're talking about is gaining bits of the passphrase to reduce the size of the brute force attack you'd need to make on it. If you're saying that providing part of the passphrase gains you anything in actual cryptanalysis of the cyphertext, you're way off.
PGP is industrial strength encryption provided you take care with your secret key and passphrase.