When someone calls or I call someone I can hear the caller but they can’t hear me volume is up all the way
Are you sure the microphone is on?
Tap to mute your end of the call (if you’re listening on a conference call, for example).
Can you use Siri? See the 'If Siri doesn't respond or asks you to try again' section in:
Use Siri on your Apple Watch - Apple Support
See if the microphone or speaker on your Apple Watch is blocked. For example, if your device has a protective case, remove it.
If callers still can't hear you, contact Apple Support.