iPhone alarm makes no sound but shows alarm screen

So I have an iPhone 6s and my alarm will do this completely randomly. I will wake up in the morning, look at my phone, and there’s the alarm screen as if an alarm was going off but there is no sound, no vibration, nothing. It’s just chillin there like nobody’s business. It’s happened somewhere between 5 and 10 time in the last month or two so it’s infrequent enough for me to still trust the alarm. This morning in particular, I was falling asleep and I was supposed to call someone so I switched on an alarm for it. Instead of going off it did nothing, and when I woke up I closed out of the alarm screen with no problem like usual and saw I had 33 missed calls. So not only did my phone not wake me up but it blocked me from 33 effing calls. I am not a heavy sleeper, there’s no way phone did ring and I just slept thru it. It was a business call and I might very well get fired over this. So apple, I’m wondering what you recommend I do, give more money to your company for a new phone, or should I throw my current phone out the window and go buy an android? Or is it just my own fault and I’m doing something wrong?