[Full question: If a man and a woman, while having phone sex, address each other as husband and wife and they actually mean it, will it amount to marriage? Even during the normal course of telephone conversations they occasionally call each other husband and wife. Does it mean they are married or is it just an over emotional sentiment?]
Doing this act is a crime and leads to a grave heinous sin which is zina (illegitimate sexual intercourse). Pronouncing the words of marriage during your conversation does not authorize this act or mean that you have made a marriage contract with that man. Marriage is a solemn contract that has its own rules and conditions without which any other kind of intimate relation is considered invalid and illegal.
Islam blocks all the ways that lead to illegitimate sexual intercourse. The Prophet (peace and blessings be upon him) said: 'The eyes commit zina, the hands commit zina and the feet commit zina and the genitals commit zina.' (Ahmad)
This is one of Satan’s traps, so repent to Almighty Allah sincerely and cut all your relations with this man. Almighty Allah says, (Do not even come close to Zina. It is a shameful deed and an evil way.) (Al-Israa’ 17: 32)
In his response to your question, Wael`Abdul-Mut`aal Shihab, a Shari`ah researcher at Al-Azhar University, stated,
First of all, phone sex and other forms of illicit relations between men and women are strictly prohibited in Islam. Those who involve themselves in such illegal practices should sincerely repent to Almighty Allah, stop all illicit relations, fear Allah's punishment, and return to the straight path before it is too late.
Just because a man calls a woman "his wife", whether on the phone or during a face-to-face conversation, it does not amount to a legal marriage. A legal marriage must fulfill the following requirements in order to be valid:
1. The marriage must be expressed in clear and unequivocal terms signifying the full consent of both male and female either in words or in writing.
2. It should be witnessed by two reliable Muslim witnesses.
3. It should also be publicized.
4. The wife’s guardian should give his consent.
5. A mahr should be paid to the bride.
Allah Almighty knows best.