Telephone sex is a poor adjunct to actually having physical sex but in the case where you are without actual physical contact with your lover it still can be pretty hot. A good imagination by both parties is a great starting place and having appropriate privacy and time to build a descriptive scenario as the primary storyteller can be very satisfying for me. But phone sex can be a wonderful learning tool where you share with your lover a story or fantasy where each of you contribute to the path the story generates.
You learn how your partner thinks and it can be a place of initial experimentation of sexual activities and ideas that you or they have not experienced but are willing to try or only want to be as pure fantasy. When a past lover lived a long way from me we would often discuss our coming encounter and create a play date from our telephone conversations from which we would gain the wonderful aspect of sexual anticipation and as the day drew nearer to to our mutual phone sex fantasy realization my and her arousal would be at a peak of need. Need to play it out but also need for each other.
Often the sexual tension build up would be so great that the moment we got to our hotel room we would simply fuck the tension away and then lie together and cuddle, talking about ourselves and how much we missed each other. Once we had connected THEN we would play out our phone fantasy.
I remember one time I was so aroused I waited in the parking lot of the hotel for her to arrive and had the wonderful satisfaction of opening the car door for her (very gentlemanly of me) and reaching down while kissing her passionately between her skirt and feeling her naked wetness against my hand knowing that she too wanted me as badly as I wanted her. She was a very good girl and never wore panties and always wore stockings for me so access was never a problem.
But walking through the hotel lobby with a raging hard on was!