Raphael Stolt recently spent some time working up a tool to visualize Phing buildfiles and he's blogged about it in this new post.
Out of the box the Phing -l option can be used to get a first overview of all available targets in a given buildfile but it doesn't untangle the target dependencies and sometimes a picture is still worth a thousand words. Luckily the Ant community already provides several tools to accomplish the visualization of Ant buildfiles, reaching from solutions that apply a Xslt stylesheet upon a given buildfile.
Using the ant2dot tool along with the Graphiz graphic library, he transforms the XML from the build file into a simple graphic showing the flow of the build. An example image is included.