Installing PHP from packages is very limited if you want more control over the version of PHP you need. For instance, the php5 package on raring release channel (Ubuntu 13.04) currently has PHP 5.4.9. If you need PHP 5.5 for your project, or (more likely) you need PHP 5.3 or even PHP 5.2 for a legacy project, you can’t use the package. It is best to compile PHP to use the version you need.