I am unable to dictate by voice a phone number after I select new message in the messaging app. I dictate the number and nothing happens after that.
Try powering off your Apple Watch and then power it back on. Or, initiate a hard reset by holding down the digital crown power button for 10 seconds until you see the Apple logo.
Are your iPhone and Watch both up to date on OS?
Try un-pairing and then re-pair.
If this doesn't work have someone test call you and answer on your Watch. If they don't hear you it may be a microphone hardware issue or something software wise effecting it.
My mic works fine. Are you able to text?...