Hi. It was hard to find but i finally found this from Lostpedia "The phone broke when Juliet attacked Charlotte inside the Tempest station. (Ji Yeon-Enhanced)".
I didn't know when the phone broke either but it broke when they had the fight.
Vicki H.
Found out when Phone broke
Re: Found out when Phone broke
I just rewatched the Tempest scene and I could find the phone anywhere.