We don't know systematically. Individuals who are U.S. citizens who have been aggrieved by a device search may sometimes file an administrative complaint seeking access to the records that were retained from their phone. That might give individuals an indication of what was taken from their phone, what records or notes were kept by the government. But we don't have a systematic policy stating what's being searched, what the search terms are, what's being retained. We do know that the government is supposed to destroy copies of information from a search if it finds no probable cause of an offence having been committed. Again, we don't know how often they find probable cause, how often they destroy information as they are supposed to according to the policy. This is all information that hasn't been revealed.
On June 15th, 2017. See this statement in context.