There are various interpretations on the origin and symbolism of the Shiva lingam. While the Tantras and Puranas deem the Siva lingam a phallic symbol representing the regenerative aspect of the material universe, the Agamas and Shastras do not elaborate on this interpretation, and the Vedas fail altogether to mention the Shiva Lingam.
Shiva Lingam as a Phallic symbol
Hinduism conceptualizes Brahman, the supreme power, as having three main roles: that of God the Creator, God the Preserver and God the Destroyer. This trinity is represented ironically by the deities Brahma, Vishnu and Shiva respectively. Thus, it is Shiva, the destructive form of the Almighty, who is represented by the Lingam or Phallus, which is manifestly the CREATIVE or generative power of Man. These points to an origin of the tradition of using the Lingam as a divine symbol that is utterly sublime in its philosophical underpinnings.
The form of the Shiva Linga serves to further emphasize this inference. The base of the Lingam is the Yoni also known as 'Parashakti'. The upright portion of the Lingam is shown as being protuberant through the yoni, and the two forms a unified structure. Thus, the Lingam represents the very instant of creation, or rather of regeneration, when the perishable and eventually destructible Old renews and regenerates itself in another form, the New that is to come.
The Tantras consider the lingam to be a phallic symbol and to be the representation of Shivas phallus, in its erect form. Accordingly, the lingam contains the soul-seed containing within it the essence of the entire cosmos. The lingam arises out of the base (Yoni) which represents Parvati according to some or Vishnu, Brahma in female and neuter form according to some.
The puranas, especially the Vamana purana, Shiva purana, Linga purana, Skanda Purana, Matsya Purana, and Visva-Sara-Prakasha, have narratives of the origin and symbolism of the Shiva lingam. Many puranas attribute the origin to the curse of sages leading to the separation of and installation of the phallus of Lord Shiva on earth; many also refer to the endlessness of the lingam, linked to the egos of Lord Vishnu and Lord Brahma.
Lingam as an abstract symbol of God
Some knowledgeable interpreters of Hindu scripture believe the lingam to be merely an abstract symbol, and point out that Lingams in many of the more important temples are not of the shape described above. Furthermore, many are the instances in Hindu lore where a sundry rock or pile of sand has been used by heroic personages as a Lingam or symbol of Shiva. For example, Arjuna fashioned a linga of clay when worshipping Siva. Thus, it is argued, too much should not be made of the usual shape of the Linga. This view is also consonant with philosophies that hold that God may be conceptualized and worshipped in any convenient form; the form itself is irrelevant, the divine power that it represents is all that matters.
Sri K. Thirugna Sambantha, in his excellent web site of Saivism, explains that the Siva lingam is the ruparupa aspect because it is neither a manifested form of Siva, nor is it formless, because the linga is a tangible piece of stone, and a symbol of God. Thus, it is intermediate between the formless Absolute, Parasiva, which is beyond the sensory perception of man, and the many manifest forms of Siva.
Satguru Sivaya Subramuniyaswami explains in the lexicon section of his book, Dancing with Siva that "Sivalinga is the most prevalent icon of Siva, found in virtually all Siva temples. It is a rounded, elliptical, anionic image, usually set on a circular base, or peetham. The Sivalinga is the simplest and most ancient symbol of Siva, especially of Parasiva, God beyond all forms and qualities. The Peetham represents Parashakti, the manifesting power of God. Lingas are usually of stone (either carved or naturally existing, svayambhu, such as shaped by a swift-flowing river), but may also be of metal, precious gems, crystal, wood, earth or transitory materials such as ice. According to the Karana Agama (6), a transitory Sivalinga may be made of 12 different materials: sand, rice, cooked food, river clay, cow dung, butter, rudraksha seeds, ashes, sandalwood, darbha grass, a flower garland, or molasses."
Swami Sivananda holds further that although the Agamas do not derive their authority from the Vedas, the two are not mutually antagonistic. Some scholars hold the view that anything that contradicts the Vedas or is inconsistent with its spirit is not authoritative. According to this perspective, the Puranic and Tantric conceptualizations are secondary to the Vedas and the Agamas which are vedic in spirit. In this point of view, the conceptualization of the lingam as a phallic symbol does not carry much weight, since the Vedas & Agamas say nothing in the matter.
Possible Biblical Reference to Lingam
There is a portion of the Bible in which the Hebrew patriarch Jacob appears to be performing something very similar to a Lingam ceremony, in which a precious substance such as milk or oil is poured on the stone artifice as a sacrificial intent. "And Jacob rose up early in the morning, and took the stone that he had put for his pillows, and set it up for a pillar, and poured oil upon the top of it." also: "And Jacob set up a pillar in the place where he talked with him, even a pillar of stone: and he poured a drink offering thereon, and he poured oil thereon." It is sometimes pointed out that the term for oil or drink used in this verse is the Hebrew Shemen, which appears like English word semen and thus seems to be appropriate to the phallic nature of the Lingam.
Of naturally occurring lingam
A lingam at Amarnath in the western Himalayas formed every winter by dripping water freezing. It is very popular with pilgrims. A stone lingam is a naturally occurring oval stone.
Shiva Lingam In popular culture
Something that resembled a Shiva linga was called the Sankara Stone in the movie, Indiana Jones and the Temple of Doom.