While we could discuss the quality of the recording, and there are a number of issues that cause the mobile phone recording to be of lower quality than the best evidence available from that DVR, there's a more straightforward reason to avoid recovering video evidence this way. If you record video evidence using the camera on a mobile phone that phone could be subpoenaed.
The Houston Police Officers’ Union warns their members, “those diabolic defense attorneys have a new one up their...sleeve”. They cite a number of situations where officers have received subpoenas for their phones. According to an article on lawofficer.com, Sgt. Richard Peña at the Los Angeles Sheriff’s Office describes the situation like this: “Every time you use a device to do something like take a photo, it’s understood that you may have to surrender that device and anything that’s in it.”
Read the Houston Police Officers’ Union article here: “Guard Your Cell Phone or Look Out for Subpoena”
Check out the full LAW OFFICER article at: lawofficer.com