Andrew Symes of Canadian Astronomy explains how.
Symes uses an iPhone, an adapter, a few eyepiece filters, and an 8" telescope.
The filters are the real trick here, because they cut down on the over-exposure you usually get.
Otherwise, Symes also recommendsNightCap, which offers manual exposure and good low light performance.
Head over to Canadian Astronomy for all his tips for taking great photos.
Smartphone Astrophotography: How I photograph the Moon & planets with my phone| Canadian Astronomy viaThe Atlantic