iPhone Photos does not provide a universal built-in collage maker for arranging several pictures into one grid. The simplest options are a collage app or a Shortcut designed to combine images.
- Choose the photos you want to use in Photos.
- Open a trusted collage app, or run an image-combining Shortcut that you have reviewed.
- Select the grid or layout you want and arrange the pictures.
- Save the finished collage back to Photos.
If you install a collage app, review its photo-access permission and give it access only to the pictures it needs when possible.
If the labels on your screen differ slightly, use Settings search or the app’s current menus to find the named feature. Apple sometimes moves controls between iOS releases, so follow the feature name rather than an unrelated setting with similar wording.