Q: Alarm not sounding

Make sure that DND is not enabled. Settings>Do Not Disturb>Off.

Also check the switch on the side of the phone. If you see orange, flip the switch the other way to enable system sounds again.

Some things you might try:

Try deleting all of your alarms, restarting, then adding the alarms back.

See if your "Do not Disturb" setting is turned on. If you see a moon in your upper right corner, it is on. Turn it off through your task bar or in Settings from the main left hand menu.

The next troubleshooting steps would be restart, forced restart, restore from back up, restore as new:

Restart your iPhone, iPad, or iPod touch - Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support

And just to be sure:

If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support