This was only one of several suggested reasons for there being 3 phones near the CS. They did not put any other emphasis on this idea, just so people who don't read the document don't get the wrong idea. JMO.
What I'm curious about is whether or not one of these three phones belonged to L, the phone we already know about. If it is, and the second phone is the phone possibly linked as a second victim phone, then that pretty much leaves the third phone as the killer's phone, an unknown witness's phone, or someone's who participated. They are saying none of these phones are affiliated with RA. My issue here is that the identity of the owner of that third phone is unknown. Does LE even know? Because if not, I'm wagering on it being a burner phone. JMO.
RA said he was looking at a stock ticker, so his phone number, linked to him via the DD interview, should have been on the trail at some point between noon and 4pm. If it wasn't, it would prove he's lying about being on his phone. Or, if it was on the trail but turned off during the murders, or was stationary the entire time, that would look suspicious. But I'm not convinced there even is any data from the trails at all, which is concerning. I think RA's phone data will be very significant, no matter if it was on or off. JMO. It could work for or against him, especially if the 3rd phone from the CS was a burner. JMO.