Are you having trouble hearing your device?  Follow these steps below to turn up your ringer volume and get an LED flash when you receive a notification. 

Head to Settings > Sounds & Haptics and adjust the Ringer and Alerts slider to set your preferred volume. You may want to disable the Change with Buttons slider; with it turned off, the physical volume buttons will only change the volume for media, like music and games.

You'll also likely want to enable the Vibrate on Ring and Vibrate on Silent options to reduce the chance of missing calls. Make sure the selected ringtone is clear and distinct.

Finally, for a visual cue, it can help to turn on the LED Flash for Alerts feature, which flashes the camera light for incoming alerts. To do this, go to Settings > Accessibility > Audio /Visual (under the Hearing header). Enable the LED Flash for Alerts slider; you can choose if it displays when the phone is on silent or not, too.