you should probably hook up that voip phone into the first router, because I don't think they really like having to go through 2 firewalls...
another option would be to disable the router inside your network (basically so it acts as a hub instead of a router), and then that router and the computers (and voip phone) will get IPs from the other router, and the problem *should* be solved..
another option: hook everything up to the first router.
another option: light it on fire and let the insurance take care of it???