Utilizing a Saved Search for the Phantom App for Splunk including a " | table _time, host, source, sourcetype, Source_IP" portion at the end of the SPL query should allow you to forward events including that field.
example:
notable search_name = “name of notable” | table orig_time, orig_source, src, dest
Event (Saved Search) Forwarding
On the Event Forwarding screen, select ‘New Saved Search Export’. The following configuration dialog will display. Fill this out as follows:
## If you’ve formatted your Splunk search output with something like the ‘table’ command, you can easily display those fields by clicking the “Auto-Extract Fields” button. This will display them below and allow you to map them to their CEF counterparts. Mapping is important as it will give some fields contextual association with actions inside of Phantom.
Note: Clicking on the “Auto-Extract Fields” button more than once will duplicate the mapped fields, check for duplicates before saving.
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