What the heck do I do with all of the phone and cable wiring in the garage?!?

To answer your question, crown is installed so only the top and bottom edges contact the ceiling and wall. It is hollow behind. Is it the best option in a garage? Probably not. With the change in humidity, it will expand and contract, which will cause buckling or gaps. Look into Wiremold. It's available from any home center or electrical supply house. It will effectively hide the loose cables and give them a finished look. Hope this helps.