That is an interesting situation. Not coming from that background, I might have a different take…
IF you are absolutely sure that 1) you asked for documentation; and 2) were not given any – and your end (i.e., your project manager agrees that you were not given any). I would be inclined to lower anxiety by first sincerely contributing to pleasant conversation on whatever topic the client appears to be willing and interested in talking about.
I would not be silent as that can be interpreted in the negative. I also would not say anything like, "why haven’t you sent us anything? We thought we would have seen the app by now and seen all the docs – what’s up with that dood?"
Open up politely. If the conversation seems to be going ok, you will find an opportunity to add…”I am really looking forward to hitting the ground running…and can’t wait to get all the specs and get going….blah blah blah. You will know that opportunity comes up when the air is hanging with “what the heck is the job?”.
Don’t worry about questions you can’t answer…like, “So what will your role be on the project?” Answer, wherever I can be the most useful …embellished a bit with particular strengths and not – how the %$#@ would I know since I don’t even know what the freaking project is?
If you really don’t know what the project details are, you really can’t be prepared to ask questions about the details, other than "what are they?"
If I were a client and actually liked people, I might want to have a get acquainted conference call where everybody met and showed the right degree of friendliness backed up by competent suitability. Of course, I am neither

, so you may want to listen to someone else.
Still, if the client leaves the conference call thinking – these folks seem like good people who are happy and have their act together, it will have gone well.
It reminds me that of all the conference calls/briefings that I have participated in, there was almost always an agenda ahead of time. The exceptions meant that I was there to listen and to listen to people that were much higher "ranking" than me.
Please do let us know how it goes.