Hello. I have some files from LineageOS's native call application, and the format is: ^{phone_number}_{date:year2}{date:month}{date:day}_{date:hours}{date:minutes}{date:seconds}. After seconds there are 3 more digits, probably milliseconds, but for me this level of accuracy is not needed. Sample filename: +48123456789_240506_225406577.amr, even if I have this person in contact book.