Hi,
According to our reporting team, the AdvertiserPhoneNumber field has been deprecated and is no longer populated. In its place, please use the AttributeValues field in the PLACEHOLDER_FEED_ITEM_REPORT to get the phone number information.
For example, here's an AWQL-based report request that will give you the phone number information for all clicked call extensions between Feb 10 2015 and Feb 13 2015:
SELECT Date, FeedItemId, PlaceholderType, AttributeValues, IsSelfAction, Impressions FROM PLACEHOLDER_FEED_ITEM_REPORT WHERE PlaceholderType = 2 and IsSelfAction = TRUE DURING 20150210,20150213
Thanks,
Josh, AdWords API Team