Praise be to Allah, and peace and blessings be upon the Messenger of Allah and his family.
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. ”
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.”
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.