But you should still check the ringer volume and the alarm ringtone.
Does Silent Mode Mute Alarms?
The silent mode does not mute alarms.

Toggle theChange with Buttonsswitch to set the volume with the physical volume buttons on the side of the iPhone.
Open theClockapp to check the ringtone for the alarm.
Tap the alarm you want to check for the ringtone or selectEditon the top-left of the screen.

Tap onSoundand confirm that the alarm sound isn’t set toNone.
Tap on an existing alarm or choose the “+” icon to set up a new alarm.
Do Alarms Go Off on DND?

Androids allow for more customization than iOS.
When you set upDo Not Disturb on Android, it’s possible for you to optionally turn off alarms.
Android phones also allow the alarm to override the end time for DND.

When you set upDo Not Disturb on iPhones, the alarm will go off at the appointed time.
FAQ
Your phone alarm will typically use your system volume.
Problems with your phone alarmcan come from a variety of sources.
Otherwise, power cycle your phone, check for a software update, or try a different alarm sound.