unclejemima,
There are two places you can change this at.
1. Under the phone extension itself.
System > Device and Feature Codes > Phones > {extension} > Flags > Auto Answer IC & Auto Answer CO: Change whichever one they don't want to auto answer on.
2. Under the Phone Related Flags and add or remove phones for those features.
System > Phone Related Information > Flags > Auto Answer IC: Add or Remove the Extension from the list
System > Phone Related Information > Flags > Auto Answer CO: Add or Remove the Extension from the list
Thanks,
TE