Things i've discovered using my phone as a dashcam.
Placement- Does it get hot where you live if so I'd be concerned about direct sunlight, also i placed mine near a vent so i can aim the vent at the iphone during hot weather or very long use.
Vibration- Depending what mount you used (I use RAM mount's) there might be a little bit of vibration during recording. If you use a window mount it depends how sturdy your mount is. Minor vibration is whatever for video recording.
Local laws- Some laws might not like dash cams or they don't mind it but they have some wire tapping law(recording audio). Thankfully iSYMDVR can disable audio to get around this issue.
Playing music- With that said, if you disable the audio recording in iSYMDVR you can play music through your phone/cars speakers.