To rebuttal this, if she did have 15 calls back and forth (I am not sure if this is confirmed from LE), given CM's age and the age of the BF, I would assume there are many text messages that are in-between phone calls. Especially if she needed a ride from him. IE; "are you here yet?", "when are you picking me up?", etc.
From other cases here on WS, it's not hard to confirm text messages from a phone number(s) without the phone. So, LE probably have that --- I would hope. If they did, boyfriend would be a POI for sure and probably being hounded a lot harder than we see currently.
That LE asked for the BF's physical phone makes me scratch my head. Don't they normally ask for phones to retrieve pictures, video and audio taped from it? That's something that cannot be retrieved from a phone carrier (unless it's stored to the cloud).
Really makes me wonder why they asked for his phone. Finding pings, texts, phone calls (the times and the lengths -- as seen in the Elvis case) are all retrievable outside of having the physical phone.