Sometimes when I receive a incoming call on my cell-phone which is kept very near to my speakers , it disturbs the speaker sound . why does this happen , isn't it safe to keep mobiles near my speakers ?
It won't damage the speaker, but cell phones' electromagnetic fields (emf) can interact with normal speakers. Speakers work with electromagnetism, with an electrically induced magnet vibrating the cone of the speaker to make sound. Cell phones use electromagnetic fields to transmit and receive calls and data.
Cell phones may also interfere with other media or signals such as broadcast TV, wifi, radio, etc. I have a baby monitor that gets interference from my phone sometimes, especially if the phone is looking for a signal.