I use a fairly inexpensive spotter and a Cannon point and shoot. The problem is ease of use. Smart phone is much better, however...
Be cautious of video frame rate. The Cannon P&S frame rate allows, with higher that desirable winds, the shot to land between frames so that the dust cloud at 1200 yards has moved too far to accurately reveal the point of impact.
Same problem with older iPhones. And the iPhone screen is a bit small for ease of use.
The best I have used is a current iPhone with something called FILMIC Pro. The older iPhone won't permit zooming video as can be done with photos.
Zooming videos and going 240 frames/sec makes SloMo quite useful and even darn fun. The whole thing is PDS (purty darn sweet).