He did not have to unlock his phone to prove he was talking to his agent. Telling his wireless company to allow CPD access to phone records would prove that. As to whether his agent actually heard the attack, how could that be proven or disproven by giving CPD the phone? Calls are not recorded on a phone.
On my phone, there’s a screen called “Call History,” or something like that, which shows what numbers called/were called and at what time. Couldn’t he just sit down with an officer, open that screen, and show that his phone was engaged with his agent’s phone at the relevant time? It would take only a few seconds, and the officer shouldn’t need to see anything else.