Since this is your first time starting sexy phone speak, you might be a little tongue-tied. But don't feel forced to say something XXX-rated. Just chat with him as you normally would and ease into a more intimate exchange by saying something as simple as "I wish you were lying next to me." Or lift his libido by reminding him of an incredibly hot sack session you had together. You're guaranteed to get a rise out of him.
If you aren't comfortable initiating a kinky conversation, suggest your boyfriend take the lead. Close your eyes and concentrate on every wanton word. As you touch yourself, fantasize that you're feeling his tantalizing fingers caressing your skin. If at first you feel shy, just moan or sigh while he narrates a naughty story. As the encounter escalates, you may be very surprised at the frisky phrases that pop out of your mouth.