Shiva is 'shakti' or power, Shiva is the destroyer, the most powerful god of the Hindu pantheon and one of the godheads in the Hindu Trinity. Known by many names - Mahadeva, Mahayogi, Pashupati, Nataraja, Bhairava, Vishwanath, Bhava, Bhole Nath - Lord Shiva is perhaps the most complex of Hindu deities. Hindus recognize this by putting his shrine in the temple separate from those of other deities.
Shiva As Phallic Symbol:
Shiva, in temples is usually found as a phallic symbol of the 'linga', which represents the energies necessary for life on both the microcosmic and the macrocosmic levels, that is, the world in which we live and the world which constitutes the whole of the universe. In a Shaivite temple, the 'linga' is placed in the center underneath the spire, where it symbolizes the naval of the earth.
The popular belief is that the Shiva Linga or Lingam represents the phallus, the emblem of the generative power in nature