What do Computer Hardware Engineers do at Apple Inc

I wish to become a Computer Hardware Engineer, I'm 14. I want know what do Hardware Engineers do at Apple. What do they do? I know that Apple makes their own System-On-Chip but they are based on ARM's Archiecture. Their displays are being supplied by Samsung for their iPhones, Camera from Sony. They don't actually make their own stuff. What is the actual role of Hardware Engineers at Apple when their Hardware componets are being made and supplied by other companies? And additionally also want to know what Computer Hardware Engineers exactly do?

Did someone hack into my phone?

Okay today I called a friend of mine and the ringing operator thingy was ringing very slowly and it has never done that before which is very suspicious but i hope it's not a person trying to get into my phone. Or am i just feeling paranoid? Leave some advice. Oh and i also have an iPhone 7 plus.

Transfer purchased ringtone from iPhone to iPhone?

I upgraded today from my 5s to a SE, and have already transferred all my apps, contacts, music, etc. But when I go into my settings to set the ringtone to the one I purchased through iTunes, it isn't there and it isn't listed in my purchases either. However, it's still listed in my purchases and tones on my old 5s, so I know I did buy it. How do I transfer it without buying it again?