@Kondwani
Consider this...
Some Dash Cam models don't film non-stop, they would more likely to loop over previous recordings, and would automatically save the video only when there is an impact (as in car crash) or when you manually press a button to save the footage (usually in the case of near-miss). Mobile phone would keep recording until you stop it.
On the other hand, if you were unlucky enough to be touching the mobile phone when a police car goes past, and one of the cops noticed you touching the mobile phone, they may (or may not) want to stop you, and question you. After all, for all they know, you could have been making calls while driving. But if they see that it is a Dash Cam, they may let you off.
Maybe a cheaper Go-Pro or an equivalent in a waterproof housing, securely fitted to the outside, would make a more clearer view compared to either a Dash Cam or a Mobile phone inside the car, that would film the mountains with the reflection of your car dashboard, objects, and even yourself, on the inside of the car's windscreen.