The level of competition has reached the limits in cellular phone market and the cellular phone manufacturers started to focus their solution in user interface. Design issues with controllability led the development and renovation of such products to the use of touch-screen phone. Touch-screen phones enhanced controllability through the instinctive use and differentiated the design by remarkable change of form factors. In this research, the controllability was dealt in regard to various grip postures, in order to improve menu layout which fits for using a thumb. Regression models were found to suggest the IDA (Iso-Discomfort Area) applying for the thumb of both hands and that of single hand. IDA indicated the level of preference (Optimum, Preferred and Acceptable) during the control of touch-screen phone. This study will allow examining the appropriateness of interface and figure out the improvement of previous touch-screen phones.