You might be interested in trying out Nitrogen[1] first. Zotonic builds on it, but picks a lot of the tools for you, so you might be interested in the basic approach first, especially if you're learning the language.
It is easy enough to start programming Erlang with Zotonic.
Every module is a completely independent gen_server, allowing you to add whatever functionality you want.
Zotonic also uses standard Webmachine resources, when you want then you can skip all functionality of Zotonic and just add whatever code you want to add or experiment with.
I would agree with that. If you want to learn Erlang, then I would also recommend Nitrogen first. It's at a lower level, so you would probably be exposed to more Erlang (as opposed to learning about Zotonic)
More basic as in working straight from the Erlang REPl, sure. Web programming is no way to learn a language, if you ask me. But I wouldn't go down much further in the web stack if you're coming from a PHP background, as it's nice to have something done quickly (And from my limited experiments with Nitrogen, you soon get some pretty neat results).
[1]: http://nitrogenproject.com/