Spam FaceTime Calls

There are other, less drastic options:

1. Put the phone on Focus/Do Not Disturb.
2. Enable Settings>Phone>Silence Unknown Callers
3. Use the mute switch (it's the little button just above the volume buttons).

Use Focus on your iPhone, iPad, or iPod touch - Apple Support

You should always use the tool that best meets your needs. If that's not an iPhone, don't use an iPhone.

Without screening your calls, there's no way for Apple to know if the call is spam or people you want to talk to. Sadly, spam in text, email and calls is a peril of modern living).