There are no settings regarding voice control in the Sonos app. Use the Alexa app to adjust the volume.

Im looking to increase the timer / alarm volume, not voice. The timer volume setting in the alexa app seems to have no effect!

If you didn’t set up the timer by voice (Alexa), why don’t use the Sonos app to set an alarm anyway. There’s no setting in the Sonos app to increase volume for a timer/alarm that was set using Alexa/Google Assistant.

I did set up the timer by voice. There is actually a setting for alarm volume in the sonos app but that didn't work either 

It works for alarms set in the Sonos app. Setting timers/alarms using Alexa is tantamount to setting timers/alarms on Amazon Echo. Sonos alarms and Alexa alarms (set up by voice) are two different things.

Not currently supported

• Playing songs based on lyrics
• Setting Sonos alarms and sleep timers
• Thumbs up/down initiated with voice is not reflected in the Sonos app
• Voice Calling
• Whisper Mode

 

https://support.sonos.com/s/article/3514?language=en_US

I know. I'm trying to set the alexa timer and have it sound loud. It does not currently. Does anyone else have any suggestions? 

Nope.

Looks like this issue will never be fixed. People started complaining about this 3 years ago: https://en.community.sonos.com/amazon-alexa-and-sonos-229102/sonos-one-alexa-alarm-volume-6793531

Pathetic.

I've sent mine back for a refund. It's a real shame as I love the sound, but it's for the kitchen and I've always got multiple timers on the go for cooking. Have gone back to my old amazon echo 

Until Update 12.1 the overall Alexa volume (voice and alarms) was much louder. Now it’s barely usable if  I dial in the volume of the music to a proper level.