Will everyone be able to see my email address and phone number?

No, your email address is only seen by the Community Manager, i.e. the PTA Chair or whoever is admin for your school's PTAsocial account. If you volunteer for something, the person managing that event will be able to see your phone number in case they need to get hold of you urgently, but generally speaking other members can only see your profile photo and short bio (if you've written one). They can still send you a message though, unless you opt out of those in your profile preferences.