Messages? You mean notifications or text messages? Cause I only received notifications and you can turn them of easily by going into your phone's settings.
I dont see where or when the Steam app tried to retrieve data other than having a cellular/online connection just like using a browser. Checked to make sure and dont see any access to camera, etc.
Anyways - nice collection of games!
But don't waste your time, I'm a very suspicious guy, and I use very few apps on my phone. You won't convince me to use their app.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.