My adviser is chairing a conference, as a PhD student how can I benefit from that My adviser is chairing an upcoming conference and I am wondering as his PhD student how can I benefit from this opportunity? 

Other than attending the conference itself and benefiting from that, I am interested in knowing if it is common for PhD students from the conference chair research group can:


review submitted papers 
help with organizing the conference
help with anything else (I am not sure if there is anything else that PhD students can help with)
Help with organizing is a great start. Do what needs to be done and don't let any task be "too low". Top volunteering spots are registration help and IT support. You can build quite a bit of good rapport by being "so and so's friendly phd student who helped get my mac to connect to the projector". Makes your adviser look good as well. Happy adviser, happy phd life. 

As someone who was in your position working with a faculty member who was an executive director of a conference, I did the following-


helped with registration
took photos
helped with general tech support issues
passed out drink tickets
whatever little thing needed to be done


In short, there is a TON to do behind the scenes at a conference to make things tick. Just be a can-do and helpful person. People notice that and it has the ability to do much more for your career than reviewing a few proposals. Those people you are helping get their mac to work on a projector might be on a search committee for a position you are applying for.