Any way to have iPhone microphone only active if sound level is above a certain threshold? I'm not sure what the proper terminology is, but I've used online gaming apps years ago where sound through microphone can be set such that it doesn't go through unless it's above a certain noise threshold.

Is this possible to do with calling from an iPhone? This would be really useful if you're calling in a noisy area because all the background noise would be filtered out . 

I have an iPhone 11.
You're describing VOX (Voice Activated Transmit), which iOS does not have as a feature.

Unfortunately there's no way to get this ability for calls.