new versions of PHP can be a pig sometimes. I find it's best to explicitly disable anything you don't need (no point in having it there if you don't need it right?). And just to be sure there's not something more at the root of your troubles it might be worth disabling most of the php options to see if it will complete an install. Probably what I would do, but then i'm no genius.
Having just relooked over the post "xml2-config path" is a path, thus one of the options inside php is probably going to be --xml2-config=</path/to/config> . "checking libxml2 install dir... no" also shows that it couldn't find the libxml2 directory.
. It contains some documentation of the xml2-config not being found and how to get around it.
This is what you are looking for :
locate xml2-config and run the above bits. /path/to/xml2-config --cflags and the --libs one.
zlib is install as one of the default options in PHP5 I believe so if you don't have it installed or you don't have it disabled it will cause an error.
You need to apt-get both libxml2 AND libxml2-dev