There are four work products in the UX design process for a software product: Information Architecture (flowcharts), Interactive Design (wireframes), graphical composition (comps) and assets (icons, favicons and more).
In small teams, one or two people often cover all these roles who are generalists. As the team grows and scales, most of the time the roles start to separate and specialize for cross-functional efficiency and effectiveness. A common separation is that the UX designer is in charge of everything up to the interactive design, and then the graphical design is done by a visual designer. However, your mileage may vary - there are many highly talented designers who can go end to end.
The boundary between designers and developers is also blurring for front end design in web and mobile development - the front end designer typically has cross-functional design and coding skills and are often highly adept at manipulating HTML, CSS, Javascript and other front-end technologies/frameworks on top of being a wizard with design software like Sketch, Figma, and Adobe Photoshop.
This article builds on content developed by the Martin Trust Center for MIT Entrepreneurship for MIT's Orbit Knowledgebase and is licensed under CC BY-NC-SA 4.0.