I always thought they were texting over the course of her travelling through the airport - more easy / discreet and (as this all seems so planned out to me) IMO he did not ring her in a panic, rather had managed to convince her to “leave her life behind” as some sort of romantic gesture, perhaps in the weeks or months before the trip. However, calling is a possibility, as is a burner phone. Hadn’t considered this.
Editing to add: if there were messages on her phone discussing some sort of plan, would she have left it with her belongings where police or family could potentially find something? This makes me lean towards having a burner phone or some other form of communication, e.g. a laptop in her carry on or something. MOO