Is there no reject call button on iPhone or something, I get a red hangy uppy button that I love for those times when someone has the gall to request my speaking voice.

If I flip my phone face down it silences the ringing. It doesn't hang up, so it doesn't give the caller any information, but it let's you ignore it easier.

On iOS hit the power button once to mute it, a second time to decline.

In my current phone pressing the lock button silences the ringing but doesn't hang up, which is what I find ideal. But I had phones that didn't just silence but did directly hang up, and it was really annoying not being able to only silence the call.

Not sure about android but it’s easy to ignore a call on iOS. If you’re using your phone when you get a call it’s just a pop up on the top that you can swipe away, if your phone is asleep when someone calls then either press the power button or swipe as if to go home.

have you tried not swiping?