After building main zxid distribution, say
make phpzxid
You MUST have php-config(1) in path. If not, try
make phpzxid PHP_CONFIG=/path/to/php-config
If the extension built successfully, you can use it by copying it to a suitable place, e.g.
make phpzxid_install
The install again uses the php-config(1) to figure out where php(1) can find the module.
Next you need to decide whether to run under Apache mod_php setup (apache), or as CGI (any web server).