There was a Forensic Files case called Video Diary. In that case, law enforcement was faced with having to enhance bad gas station surveillance video. In that case, they were able to enhance it enough to use it to make a positive identification of a suspect.
Here is the difference. In that case in Michigan, when law enforcement made their sketch(which led to a phone call tip and an arrest), they used the enhanced gas station surveillance video.
In the Delphi case, law enforcement is relying on eyewitnesses who may or may not have seen this man leaving the Monon High Bridge area. Their strategy has not worked out so far because eyewitness descriptions are sometimes not very reliable. In my opinion, they are not using Liberty German's phone because they probably cannot enhance the video enough to make a solid sketch.
So, in my opinion, the answer to your question is that law enforcement does not have enough details from the video on Liberty German's phone in order to give an accurate description of the offender in this case.