It’s obviously a stupid idea…

“I can’t always even hear my phone ringing when it’s in my pocket, but it expects to be able to hear something “ringing” some distance away?” – there, you’re comparing your ears to the microphone on the phone, which doesn’t make that much sense – they work differently (the phone is not using related neurones for other things, for one). I wonder if the muffling effect is the same if the source is outside but the receiver is inside the pocket? That’s more like putting your head in your pocket, really. Would you be able to hear a phone at head height if your head was in your pocket?

I agree that the microphones might not be so good at high pitched frequencies, given that they were designed to pick up human voices – but they might have got lucky I suppose. Also, it’s possible that higher pitched sounds are less dampened by surroundings (but maybe frequency only affects that sort of thing for transverse, not longitudinal, waves – I don’t really know!)

All in all, you had me at “it’s a bug” tbh.