What is the ruling on the clear white fluid that is discharged after a phone conversation with one's fiancée, and does it necessitate Ghusl (ritual bath)?

What came out of you is madhy (pre-seminal fluid), which is impure (najis) and nullifies wudu (ablution). It does not necessitate ghusl (full ritual bath). It suffices to wash the area of the body and clothing that it touched. As for your fiancée, if the shar'i (Islamic legal) marriage contract has been concluded, she is your wife, and you may speak with her freely. Otherwise, she is a stranger (ajnabiyyah), and it is not permissible to speak with her except within shar'i guidelines.