This paper proposes a new strategy to improve the reliability of phased mission system (PMS), namely by swapping of components. In the proposed strategy, when a component fails, it can be swapped by another one in the system which is still functioning. We consider both the options to swap components at any time and for swaps to be possible only at phase transitions. This paper also discusses the strategy of swapping components according to structure importance. The structure importance is used to measure the importance level of the components in contributing to system reliability. Then when a component with high importance fails, it is swapped by another component with lower importance from the system which has not yet failed. The survival signature methodology is implemented to assess the reliability of PMS when there is a possibility of components swapping. In addition, we consider the cost effectiveness of component swapping through two models (time independent and time dependent) of penalty costs of PMS.