Lorna Mitchell has a quick post to her site today showing you how to link up Travis-CI and phing to execute the phing build on the Travis-CI service.
We've started using Travis CI on one of my projects to run some build processes to check that everything looks good before we merge/deploy code. One thing I ran into quite quickly was that I wanted to install phing in order to use the build scripts we already have and use elsewhere, but that it isn't provided by default by Travis CI.
To get it all cooperating, she uses the "before_install" settings/functionality Travis provides to use PEAR to discover and install phing. Then in the "script" section, the build can call the phing executable without problems. She does point out one "magic" kind of thing that rehashes the Travis environment and lets to know phing exists: the...well..."rehash" configuration setting.