Can a police officer answer someone’s phone and pretend to act like the owner of the phone or the owner’s friend?
The short answer is yes. Someone can answer the phone who is an officer and give let's say directions to the persons's phone. If the caller doesn't ask the person to identify himself, and/or if the officer is undercover, there is no entrapment issue because the caller is already prone to committing the crime. It is entrapment, however, if the officer coerces the other and pushes the person into committing a crime (let's say a drug deal or prostitution deal). Calls often happen during drug raids, wherein the officers have already secured the property and arrested the individuals involved, during a warrant search or seizure.