A phone can struggle with moon photos for two main reasons: focus and magnification.

First, try manual focus or focus as far away as possible. Autofocus may miss and leave the moon soft. If your phone allows it, set focus to infinity.

The bigger limitation is lens reach. Most phone cameras use a wide lens (roughly 24–28mm equivalent), so the moon appears very small in the frame. Digital zoom only crops the image, so quality falls quickly. For detailed moon shots, people typically use much longer focal lengths—roughly 300mm to 1000mm or more, and sometimes 600mm to 2000mm equivalent.

If your phone has a strong telephoto lens, that may help a little. Otherwise, a superzoom/hyperzoom camera is a more practical option for moon photography than a basic phone camera. Another route is attaching a camera to a telescope for more serious astrophotography.

So: try manual/infinity focus first, but for clear, detailed moon photos, the main thing you need is much more optical zoom than most phones have.