What is the significance of Linga svarupa compared to Moorthi svarupa of Lord Shiva Why we see so many lingas all around the world What is the significance of the linga svarupa or shape
In Shiva Purana Bhagawan Shiva said to Lord Brahma and Lord Vishnu the following.:
madātmakamidaṃ nityaṃ mama sānnidhyakāraṇam | mahatpūjyamidaṃ nityamabhedālliṃgasiṃginoḥ || 43 || yatrapratiṣṭhitaṃ yena madīyaṃ liṃgamīdṛśam | tatra pratiṣṭhitaḥ sohamapratiṣṭhopi vatsakau || 44 || matsāmyamekaliṃgasya sthāpane phalamīritam | dvitīye sthāpite liṃge madaikyaṃ phalameva hi || 45 || liṃgaṃ prādhānyataḥ sthāpyaṃ tathāberaṃ tu gauṇakam | liṃgābhāvena tatkṣetraṃ saberamapi sarvataḥ || 46 || (Sri Shiva Maha Puranam 1:9:43-46).
The phallic symbol and the symbolised Śiva are non-different. Hence this phallic emblem is identical with me. It brings devotees quite near to me. It is worthy of worship therefore. O dear sons, if phallic emblem of this sort in installed I can be considered installed, though my idol is not installed. The result of installing the phallic emblem is the attainment of similarity with me. If a second phallic emblem is installed, the result is union with me. The installation of the phallic emblem is primary and that of embodied idol is secondary. A temple with the embodied idol of Śiva is unfructuous if it has no phallic image.
I hope this clarifies your queries.
Why is Shiva worshipped as a Lingam?
The answer is that the Saivites use the linga form to signify nameless and formless aspects (Niskala) of the deity.
Sages said:- 8. Everywhere the deities are worshipped only in their image. How is that Siva is worshipped both in the image and the linga?
Suta said:- 9. O sages, this question is holy and wondrous. Here the speaker is Siva Himself and not any ordinary person. 10. I shall tell you what Siva Himself had said and what I heard from my own preceptor. Siva alone is Niskala (nameless and formless) since He is identical with supreme Brahman. 11. He is also Sakala as He has an embodied form. He is both Sakala and Niskala. It is his Niskala aspect that the Linga is appropriate. 12-13. In the Sakala aspect the worship of His embodied form is appropriate. Since He has the Sakala and Niskala aspects He is worshipped both in the linga and in the embodied form by the people and is called the highest Brahman.
Shiva Purana, Vidyesvarasamhita, Chapter 5
Where does the linga form come from?
The day on which I manifested myself in the form of a column of fire is the Ardra star in the month of Marga-sirsa (November-December), O children.
He who sees me on the day of Ardra star in the month of Margasirsa in the company of Uma and worships my Linga emblem or embodied image is dearer to me than even Guha (Kartikeya)
On that auspicious day (Sivaratri) the vision alone accords ample results. If he worships too, the result cannot be adequately described.
Since I manifested myself in the form of Linga emblem in the field of battle, this place will be known as Lingasthana.
O sons, this column without root or top will henceforth be diminutive in size for the sake of the vision and worship of the world.
The Linga emblem confers enjoyment. It is the only means of worldly enjoyment and salvation. Viewed, touched or meditated upon, it wards off all future births of the living beings.
Since the Linga emblem rose high resembling a mountain of fire, this shall be famous as Ruddy (Aruna) mountain. Many holy centres will spring up here. A residence or death in this holy place ensures liberation.
Siva Purana, Vidyesvarasamhita, chapter 9.15-22
What is the philosophical meaning of the Linga?
Shiva Linga according to Shiva Purana represents an infinite tower of light and is used to represent nishkala (formless) Shiva. Linga means mark. Shiva Linga simply means a symbol of Shiva. The Yoni associated with the Shiva Linga is simply the source. Just as Vedantins have Brahman - Shakti, Sankhya has Purusha - Prakriti, Shaivism has Linga - Yoni.
O highly blessed ones, at your entreaty I shall mention it to you after bowing to Uma and Siva.
She is the mother of the universe. She is named Bhaga. She is the three-fold pedestal of the deity in the form of a Linga.
Linga is the lord himself. O excellent brahmins, the creation of the universe is by both of them. Siva in the form of a Linga is the splendour stationed above darkness.
In view of the union of the Linga and pedestal he became Ardhanarisvara (Lord with the form of a woman in one-half). At the outset he created his son Brahma the four-faced Lord.
Linga Purana II.99.6-8
The Linga is equivalent to Brahman of Vedanta. The word linga is traced to two Sanskrit roots, li meaning to dissolve and gam which means to go, to be manifested or created. The Sivanubhava Sutra 3.3 defines Linga as follows:
That in which all mobiles and immobiles enter, i.e., get dissolved, and that from which the universe is created is Linga.
Sivanubhava Sutra 3.3
…The Linga is spiritual knowledge and is stationed in the hearts of Yogins.
Kurma Purana II.11.94b-95a
I have posted below some additional shlokas from Linga Purana that will hopefully be helpful in understanding Shaiva thought on linga.
Linga is so called because, O gods, everything gets dissolved in it.
Linga Purana I.19.16
The Linga is pure, auspicious and imperishable. It is exceedingly blissful in nature. The Niskala form, that is, the form devoid of attributes is all-pervasive. It is always stationed in the heart of yogins.
Linga Purana I.75.18
O brahmins, they say that the Linga is of two types viz., - the external and the internal. O excellent sages, the gross one is the external. O brahmins, the subtle one is the internal. [So are the devotees.]
Linga Purana I.75.19
The gross devotees are those engaged in the worship of gross lingas and interested in holy rites and sacrifices. The gross idol is just for awakening knowledge of the gross devotees.
Linga Purana I.75.20
The spiritual Linga is not perceptible to the deluded person who conceives things only externally and not otherwise. The gross linga made of clay, wood, etc., is perceptible only to non-yogins as the subtle and eternal linga is perceptible to the Jnanin.
Linga Purana I.75.21-22
Niskala and Sakala Siva are not two
Other knowers of reality say that the object, on consideration, is non-existent.  Therefore, everything, the Niskala and the Sakala is of the nature of Siva.
Linga Purana I.75.23
 arthah – goal, viz. the release from the bondage of activities. Because, actually, as there is no bondage, there is no release. Cf. Pancadasi.
Various types of Lingas
There are also mukha linga or Lingas with faces. Then there are vigraha Lingas where the full form of Siva is inscribed on the Linga. The faceless Lingas are called Sthanu Linga or Linga columns which form is traced to legendary material about Shiva given in certain Puranas like Linga Purana (ch 17), the Kurma Purana (I.26.68-99) etc where Shiva appeared as a column of fire.