My take on the phone involvement at Moonflower is that Brian was worried that Gabby was about to leave him there without his phone (according to what he told the officer), so he was attempting to grab hers so that she wouldn't go, or so he'd have a phone if she did go.
As far as things ramping up by 08/25, it seems they were absolutely under a lot of stress from the close quarters of the trip, the inability of Gabby to get as much work done as she wanted, and according to what Brian told the officer, Gabby was upset with the bugs. I also wonder if Brian was unhappy about the potential meet-up with Gabby's friend at Yellowstone in the next few days. Apparently, they were planning to go there on the 27th. I'm guessing that Rose never made the trip, but I don't think that's been confirmed.