Smartphones can be used to image the moon by holding it next to the eyepiece of a telescope. For smart phone cameras, a mid-power eyepiece such as a 25 mm eyepiece yields good results. To hold the phone camera steady while taking a photo, a smartphone-to-telescope adapter may be used.
This imaging method is called afocal imaging, in which a camera with its lens is mounted next to another image-forming optical system such as a telescope with an eyepiece or a pair of binoculars.
Related link: Universal Camera Adapter
Night Sky in Focus Astronomy and Amateur Radio © Anthony Urbano (Manila, Philippines)