Does this seem normal? I can’t believe it is using that much bandwidth for 10-15 calls during the same hour?
No Love… 
Not sure I’m understanding what your question is.
I don’t know what’s going on with your 172.16.x.x network, so I can’t see how I can give you any advice.
If I assume your phones are on that network along with a bunch of servers and other stuff, the network diagram could be perfectly normal. It’s really impossible to know.
You can run a tcpdump on your eth[01] port on the server and watch the traffic to see if there’s anything goofy.
Thanks Dave, I was thinking that was just phone traffic since it was showing on my asterisk server, but yes, we have basically everything on that 172.16.X.X network, no vlan, I know I should do it. I just don’t understand it well enough to do it without totally redoing our network, and in the process taking everything down for too long, we are up 24/7, so maintenance is a real struggle.