While I am speaking with my fiancé on the phone, some seminal fluid is discharged from me. Do I have to perform ghusl?

Ghusl (definition) (ritual bath) is obligatory if the fluid discharged is semen and lust was experienced, based on the Almighty's saying: "And if you are in a state of janabah (definition), then purify yourselves" (Quran 5:6), and the Prophet's (peace be upon him) saying: "Water is from water [i.e., ghusl is required after seminal emission]." Scholars have agreed upon the obligation of purification upon the emission of semen. It is also impermissible to speak with a suitor in a manner that arouses lust.