I am not saying that something should be reversed - I just don't understand what you're trying to do and how your configuration is supposed to work. Based on your description, your configuration is as follows:
- your SIP phones are registered with some SIP provider (not with UCx)
- inbound calls are routed from the SIP provider directly to the SIP phones (UCx is not involved at all)
- outbound calls are via UCx as the proxy
Now, this contradicts with the title of this thread - if your SIP phones are down (I assume you mean not registered), they are not registered with your SIP provider - UCx has absolutely nothing to do with it. You should contact your SIP provider to find out why.
In my opinion, a typical configuration of UCx with SIP phones and SIP trunks from a SIP provider should look more like this:
- SIP phones are registered with UCx as SIP extensions (i.e., UCx is the configured SIP server)
- SIP phones do not use any outbound proxy (they use UCx where they are registered)
- SIP trunks from a SIP provider are registered on UCx as trunks
- inbound routes are configured on UCx to route calls to SIP extensions (phones) based on DID or in some other way (ring groups, IVR, etc.)
- outbound routes are configured on UCx to allow SIP extensions (phones) to make outgoing calls over trunks
You mentioned that you have 2 Nortel phones. If these phones are functional, you already have the inbound and outbound routes configured to allow these two phones to receive/make calls. It sounds like all you have to do is to reconfigure your SIP phones to register with UCx and you should be able to make/receive internal and make external calls. To receive incoming calls from the SIP provider for trunks that were used so far directly by your SIP phones, you should add corresponding SIP trunks to the UCx configuration.