Is Phone Sex Between Spouses Allowed?
Question

Is it allowed for a married couple to speak through the telephone about sex and to excite each other so much that one of them or both get an orgasm (without their hands, because that is not allowed)?
This happens because the man is living abroad for work and they see each other only once every four months and they miss each other very much.
Praise be to Allah.We put this question to Shaykh Muhammad ibn Salih al-‘Uthaymin, who answered as follows:
“There is nothing wrong with that. Yes, it is permissible for spouses to talk to each other about sex over the phone. ”

Question:

Even if there is use of the hand?
Answer:
“There are some reservations about use of the hand (i.e., masturbation). It is not permissible unless one fears that one may commit zina otherwise.”

Question:

So as long as there is no use of the hand, it is OK?
Answer:
“Yes, as long as there is no use of the hand, it is OK. He can imagine that he is with her and there is nothing wrong with that.”
They should also make sure that no one is listening to what they say or is spying on them. 
For more about sex in Islam, please see these answers: 5560 , 1202 , 108872 , and 91968 .   
And Allah knows best.