Why did she connect to the other phone with bluetooth?

She wanted them to be alarmed and stop but they saw her anyway. She should have yelled and ran before the stabbing but she was too scared and didn't know what to do. Apparently they didn't have a signal and it was a way for the phone to make a noise.

She had the GPS that was paired up to Steve's phone, not a phone of her own. The call was actually being made on his phone through the GPS. Steve told her to take it after the crash so she could find her way out and get help. I still can't figure out why his phone would vibrate while making a call though...

Two, wasn't her phone, didn't vibrate just showed the antagonists that she was still in the area and calling 999. Did I miss why she herself didn't have a mobile phone?

She didnt connect her phone to Steve's phone, it was the Sat NAV they were using on their way to the lake. Since Sat Navs don't have calling facility, she paired it with Steve's phone to get the calling facility.