Your phone will make audible alerts based on your phone’s push notification sound settings when a video analytics rule sends a notification.
Make sure in your video analytics rule that your desired push recipients are selected and make sure on your mobile device that your notification sounds are not muted.
Here is a guide showing how to set up notification recipients within the video analytics rules:
Do you get audible alerts for any Alarm.com push notifications on your phone? What model of phone and operating system version are you using?
In case you are not getting any push notifications: