A pilot deviation is a term used when a pilot deviates from an ATC clearance. Actions such as climbing/decending through an assigned altitude, not complying with a radar vector, or even deviating from the route of flight for which an aircraft was cleared (without notifying ATC).
Sometimes these deviations can result in a loss of separation which is pretty serious. The phone number was probably to the watch supervisor's desk at the ATC facility in an attempt to obtain more information about the incident.