Hi.
When you enable "run on all active nodes" you let the ip phone to use the CUCM where it is registered on to call out.
Verify that on your VG you configured dialpeers for all CUCM nodes.
Here is a very useful doc written by my friend Deji https://supportforums.cisco.com/blog/12088366/sip-trunks-and-run-all-active-cm-nodes
Give a look as far as you can.
HTH
Regards
Carlo
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