It is incredibly difficult to hold binoculars steady enough with only your hands, even if using a quality mount, to get a shot in focus with your phone peering through the scope lens. Best advice is definitely to get a tripod and adapter.
The 8x42s are going to bring in considerably more amounts of light and thus will produce a sharper image on your phone than a 8x25. Plus they are better for birding, esp if you want to start doing sparrow ID :)