Lync Device Update Service is a way to manage Lync phones firmware through Lync (its really rather simple once you run through it one time). This article will specifically address phones in a multipool environment. Jeff Schertz does an outstanding job outlining how updating phones work in a single pool environment.
I originally thought once you uploaded the firmware into Lync, Lync would replicate the required files to all appropriate pools. In my environment we have a total of 4 pools to which I control 2 of them (note the 2 pools I Administer are resilient). To my surprise, I was pleased to find the import-csdeviceupdate only updated one of the paired pools. So what does this mean? It means I can control updating phones on my Lync Pools without having to work with the Admins of the other 2 pools.
In short, if you have multiple pools and each pool will have phones registered to it, you will need to import the update per pool, then approve the updates per pool.