.pgbomit is a file that you can create and add to a directory that signifies to PhoneGap Build that it SHOULD NOT
include the contents of that directory as source for the native applciation. This folder, however, can be
used to store any files needed during the PhoneGap Build process up to the compile step.
A typical use case is for a directory containing the icons and splashcreens for an app. Place .pgbomit in that directory and none of those files/directories will be included in the binary app package, except those copied and used for icons and splashscreens for a specific platform.
Please note that the .pgbomit file is a placeholder file only, it is not read and its only function is to highlight a directory. It is not like .gitignore or other file types that can contain patterns.
.pgbomit
http://docs.build.phonegap.com/en_US/introduction_getting_started.md.html