We demonstrate the physical mechanism of optical Tamm states using the phase properties of the photonic crystals. Based on such mechanism, we propose an efficient way that can precisely produce optical Tamm states at specific frequencies. Moreover, we show that dielectric photonic crystals and single-negative materials can be effectively connected through their reflection phase. Two kinds of one-dimensional dielectric photonic crystals with different single-negative characteristics are designed and repeated alternately to construct a superlattice structure. The band structures and the transmission spectra of this superlattice show that multiple optical Tamm states arise and these Tamm states are coupled with each other to form transmission bands. A special zero-effective-phase gap can also be observed in such superlattice.