Install phonak app on Apple Watch
The phonak App does not appear on Apple Watch app after downloaded to iPhone
iPhone 11 Pro, iOS 17
Are you asking about the myPhonak app for the iPhone?
That app's page in the App Store shows that it is an iPhone-only app.
M1 Mac mini, macOS 14.4.1; Watch, series 7 GPS/cellular, watchOS 10.4; iPhone 12 Pro, iOS 17.4.1; TV 4th Gen, tvOS 17.4; HomePods, audioOS 17.4 and Airport Express w/ Airplay 2