Dotsie,
I don't know of any specific studies correlating panic attacks (in women) with the fact that women have 24/7 jobs. But it's clear that there's a general link between stress/overload and incidence of panic attacks. Panic attacks did not become an "official" diagnosis until 1980, and boomer women entered the work force long before that. But stress is a definite and recognized trigger for panic attacks, so, study or no study, the fact that women often have to balance so many things in their day certainly takes it toll on anxiety levels.

Dianne,
An anxiety attack is a specific, so called "discrete" event that last for a certain length of time and has several symptoms associated with it. A phobia is a particular fear - of an object (like spiders), an act (like public speaking) or sometimes even of people in general (called "social phobia.") It may happen that a person who experiences increasing anxieties might go on to develop phobias, but from a diagnostic point of view, the current thinking is that it's the other way around - that a phobia causes anxiety: a person who has a strong phobia, one that interferes with their daily living (like driving, for instance), might experience anxiety attacks because of the great fear they carry around inside of them. If you have a phobia of bridges, and live in Nebraska, you probably won't develop anxiety attacks because you probably don't have to cross bridges (not literally, anyhow) everyday. But if you lived in Bridgetown U.S.A., it'd be tough times on a daily basis, and the phobia of bridges would be assaulting you everyday and probably result in your developing panic attacks.

As to "why so many different phobias?" - it's a mystery. There's like thousands and thousands of phobias listed in the Encyclopedia of Phobias. But (aside from obvious cases) no one knows the exact reasons why one person develops phobias and another lives a phobia-free life.