Smartphones are widely accessed by all genders, ages, and statuses with the increasing use rate of older adults. When people grow up to older adults, they meet physical declines such as blurred vision, tremor in hands, and arms, slowness of movement, or postural of a humpback. These age-related conditions affect how they live and use the smartphone. However, some seldom go out for older adults' activities due to their physical impairment and diseases. They might have lower competencies than normal older adults. In this article, the test was conducted on 26 homebound older adults. The current investigation was concerned with their competencies of vision, hearing, touching, and memorizing to find appropriate average results for them. We found the scores value regarding font size, color contrast, icon size, a touching point on each button on the screen, keyboard's size, scrolling area, etc., which they can perform effectively on the smartphone. The main findings render a significant and unique contribution to the design community to use it as a guideline or standard for every designer who wants to design assisted technology by using a touch screen interface for home-bound older adults to conveniently access and efficiently use. Further, it also helps to improve the quality of life among older adults.