Aphrodite's’ place in the pantheon of twelve Greek gods that reside at Olympus suggests that she is an important deity to the Greeks. There were several reasons the Greeks worshiped her. She was the goddess of love and passion, two qualities that all humans share. She was known to be the protector of sailors, which was an important endeavor to the Greeks. As the goddess of fertility, the Greeks saw her as important to replenishing the population through recreation. The Greeks also adored her because of her intense beauty and attractiveness. She was irresistible to both gods and humans and was said to have had relationships with both. As the goddess of love, Greeks believed she could bring peace and civility to the world.
The Greek poet Homer paid homage to Aphrodite in the Illiad. When Paris was given the choice between victory in battle, eternal wisdom, or the beauty of Helen offered by Aphrodite, he chose the latter. This decision led to the Trojan War, and is a reason the Greeks most likely feared Aphrodite.
Aphrodite was so beautiful, that she could influence men in this way. The Greeks wondered if her intensity could cause men to make bad decisions. She is the ancient femme fatale. Few gods could resist her power, so how could human males be expected to resist her charms.
The Greek deities were anthropomorphic, which meant they had human qualities and emotions. When angry, they could act out toward the humans with disasters. In addition to her charms, Aphrodite is known to be ill-tempered and could be offended at the slightest misstep. When you consider this, it would make sense that Greeks want to keep her happy.
Aphrodite is the Greek Goddess of beauty. It is human nature to be attracted to things that are beautiful. So of course humans are drawn to her, But then of course since she is the goddess of beauty they worship her for other reasons. Just about everyone wants to be skinnier, tanner, etc. So the Greeks believe that if they worship and praise Aphrodite the goddess of beauty, they will become beautiful which makes sense.
As for the next question- why do they fear her?
Well if she makes you pretty for praising her think what would happen if you didn't praise her. Most likely the opposite. The opposite in this case would be making you ugly. And this wouldn't be the first time Aphrodite has done something like this. She made Medusa, who was once beautiful, so ugly you turn to stone just from looking at her. So, they fear she will do the same or something equivalent if they don't worship her.