Phone calls are considered "personal communication" in APA style.
Because they do not contain "recoverable data" - meaning, no one else could go 'look it up' after the phone conversation is over - these are not included in the reference list at the end of the paper. However you can include it as an in-text citation.
Personal Communication includes letters, phone calls, email messages, and interviews.
APA Style In-Text Citation:
(Interviewee First Initial. Second Initial. Surname, personal communication, Month Day, Year)
Example: (A. Smith, personal communication, September 27, 2013)
References:
Do not include in your references list.