One great way to spend a phone date is to make a plan to do the same activity while you're talking on the phone together. Plan a fun and easy activity that you can do around the house, and just chat on the speaker phone while you do it. It'll be almost like you're together, even if you're not.
Watch the same episode of your favorite TV show, or a big game, and talk about it while you're on the phone. Cue up your favorite movie. Even if you have to be quiet most of the time, it'll be almost like you're together. Try out a recipe together and try to make it at the same time. Talk each other through it and laugh at your successes and failures. Text each other pictures of the end results when you're done and see who made it better. If you can, Skype or other video-chatting makes this even better. Even if you're not saying anything, it'll be like you're in the room together.