Vinoji,
There are two components to chanting any mantra.
1. Your state of mind / the purity of your mind with which you chant the mantra.
2. proper pronunciation.
The main reason there is often emphasis on getting mantra initiation from a guru is so that you are chanting / pronouncing it correctly. It may not be a bad idea to learn from a pandit or someone else on correct pronunciation, however I do not believe it is necessary to get formally initiated.
More importantly your state of mind, your faith has to be firm and pure. You can recite any mantra correctly thousands of times but if you don't have purity and a firm faith in the mantra mantra it will not be effective. Therefore, this is much more important than anything else.
Begin you chanting on a Monday. Pray to Lord Shiva that you overcome your phobia and chant away. You will see the results.