I have never use bsd.
But it may be because when you do the OS installation, some library is not installed so that when directadmin try to compile php, it was unable to compile the php source code, ie. unable to create the php binary.
You should manually recompile the php source to see if there are any error message during the compiling.
under the customapache directroy, there should be a folder something like php-4.4.8, just go into the directory and type "make" to see if you see any error message.
That is my guess though