Phallic means resembling or related to a penis: people often talk about phallic shapes, like the Washington Monument.
When you see phallic, think penis. Calling something phallic means it's penis-like in some way. In some cases, that means it has creative power, like how a penis, through sex, creates new life. In other cases, people just mean it looks like the shape of a penis. Many people have looked at phallic shapes in the world — such as missiles and many sculptures — and wondered what exactly the creators were thinking about.