Walkie-talkie is not available
When I try to download a walkie-talkie on my iPhone, I get the message "Applewatch needed" When I try to download on Applewatch it says that I need an iPhone
Apple Watch Series 9, watchOS 11
The Walkie-Talkie app is part of the watchOS. You should not need to download it. Otherwise, your iPhone is almost out of charge, it will not download anything with the battery in the red zone. You can find the Walkie-Talkie app on the Watch.
You can see this support document for information about the Walkie-Talkie app. Use Walkie-Talkie on your Apple Watch - Apple Support
Also, the walkie-talkie is not available in all regions. See the link I provided above to see if your region is supported.