A flexible, stretchable, and adjustable strap that is designed to be used with most commercially available smartphone cases to assist the user in holding and using their smartphone is provided. This strap is easily installed on and removed from such cases in minutes, without
adhesive, modifications to the case, or any structure permanently attaching the strap to the case, allowing the user to use the same strap on a different case or to change straps without the need to purchase a new case. The strap, consisting of a stretchy / elastic material with hook and loop fasteners on each end that enable connection to form a loop through the existing ports on the case, is positioned to lie flat and tight against the back of the case and may be stretched from this resting position to accommodate the user's fingers, hand or other objects to steadily hold the cased smartphone. In addition to the improved functionality provided for smartphone use, the strap is designed so that logos remain visibly identifiable / recognizable and only minimally or not at all deform upon stretching the strap during use and non-use, which provides a new medium for personal expression and unprecedented promotional and advertising value to companies and organizations to connect with their customers or members and to reach potential customers and members by using the strap to identify their name, brand, message or other logo that they seek to promote.