Can a lightning cable of a different country damage the iPhone?

Hi,

I'm an iPhone users for 6 years now and I love the product itself. Last December I was gifted with an iPhone6 but since then I had to substitute the phone twice because of hardware problems. The first time the phone switched off and on by itself randomly during the day, they sent me a new one and after 20 days I had to ask for a new substitution because the phone switched off by itself for good (doesn't turn on even if I plug it into a computer or if I force the re-start).

Now, I'm wondering if the iPhone6 is so badly made (never had a problem with iPhone 3 and just had a problem once with iPhone 5) or it's something that depends on me.

I try to follow all tips for iPhone users but lately I'm wondering if it's something that depends on lightning cable. I read that fake cable can damage the phone, I use just original cables but the one I'm using ATM I bought in the US (I live in Italy). It could be that a cable from a different country (maybe with a different voltage) even if original, may damage the phone?

Thanks!