try to use the phone without any other devices running on the remote site.
Best would be of course a network assessment to know if your bandwidth is sufficient at all times but short of that try it that way. If you still have bad quality then it might just be the delay on the connection.
I suspect that you have the connection straight over the Internet, or do you have a rented connection? If so then there might just be congestion between the points.
Actually I just thought of it, maybe the congestion is at the main site so if you can monitor the bandwidth used at the main site do that too.
Joe W.
FHandw., ACS
If you can't be good, be good at it!