Ehh -- I'd just reconsider the 'literally all' part. There are alcoholics who just chase the feeling for itself -- a quick fix for sad thoughts, but not for all. It's a complicated disease, but some with issues crave booze regardless of how they're doing mentally. At least in my somewhat limited experience.
I am an alcoholic and for me it's more you replace any activities outside of work with drinking as a substitute for doing stuff. Later you realise you didn't just replace activities alcohol replaced people too. So in the end all I had to do was drink.
Uh, that doesn't mean it isn't true. Alcoholics don't drink for no reason. (Source: had to quit drinking because of the problems it was causing for my life.)
Of course not. Nobody does things for "no reason." It's more that sometimes we don't understand the motivation. With alcoholics (and drug addicts in general), my guess as to the reason is that it feels good, or otherwise does something for them. I've been told one's first time doing heroin or smoking crack is pure heaven. People who quit generally do so because it causes secondary problems for them. And, that makes sense to me, because why quit something that feels good, but doesn't cause any other problems?
Most of this is pure speculation and extrapolation from my own experience. I had a short period of time when I was drinking excessively to deal with work stress. Once I noticed, I was able to stop, because I knew it would cause me problems later on. Luckily, I never suffered any health effects or legal issues from it, mostly because it was only about a 2-3 week period when I would drink every day after work.
Switch "on my phone" with "drinking alcohol" and that's literally how all alcoholics think.