User profile for user:
Community User
On the phone;
Go to: Settings/Siri & Search - check the all desired settings are enabled.
Go to: Settings/General/Restrictions - check that the restriction for Siri & Dictation is not enabled.
Go to: Settings/General/Keyboard - check that Enable Dictation is turned on.
On your Apple Watch;
Go to: Settings/General/Siri check that Hey Siri is turned on.
To use Hey Siri on Apple Watch, the display must be awake.