is the callerid set in campaign is not showing or the callerid set in dialplan not showing?
According to your config your dialplan is setting the callerid , so it will discard the callerid set in campaing.
as per your dialplan the second line setting the callerid
exten => _7878X.,n,Set(CALLERID(num)=${EXTEN:4:7}${RAND(1001,9999)})
it will set callerid by discarding the 7878 and adds a random number between 1001-9999 before the number you have dialed.
eg if you have dialled 78781234567 then callerid will be 10021234567
to check what callerid is set , use the below dialplan and check cli logs.
exten => _7878X.,1,AGI(
agi://127.0.0.1:4577/call_log)
exten => _7878X.,n,Set(CALLERID(num)=${EXTEN:4:7}${RAND(1001,9999)})
exten => _7878X.,n,NoOp(MY CALLEID IS ${CALLERID(num)})
exten => _7878X.,n,Dial(SIP/Phonix/${EXTEN:4})
exten => _7878X.,n,Hangup()