Try verifing if you have enough tone generators.
"li meas tone sum today" will show if you have any failures.
I am having the same problem (2 to 3 phantom calls a day) and the only issue I have found is that we are having DTMF and CC-TTR tone failures. Avaya hasn't been able to say if the two issues are related but it maybe. When we upgraded to S8700 Avaya removed all tone cards and classifier cards, they are shipping me a classifier card to see if it resolves the issue.
I have checked vectors, queue length, events & trunks and have not been able to find a solution.
Here's what's happening in my situation;
The caller enters the first vector:
1. wait time 2 sec hearing ringback
2. collect digits after announcement XXXX
3. route to number 1234 if digit = 1
4. route to number 2345 if digit = 2
5. route to number 1234 if unconditionally
6. stop
from this point they believe they are going into a queue because they hear hold music. Since this vector doesn't deliver them to a queue and the calls aren't showing up in my CMS reports I don't believe they are queued but held "somewhere". I have been able to track down the calls using Nice Anaylzer craddle to grave reports, it shows the call hitting the VDN/1st vector, states it is queued and than disconnect when the caller finially hangs up. What is odd is the report shows the call never leaving the 1st vector and though it says it queued doesn't provide any queue information.
I have contacted Avaya and they are not aware of any issues and there are no patches for this problem. I'll let you know if the call classifier helps.
good luck,
smartinmich