I think the biggest hurdle I used to have with phone calls was knowing when was a good time to call. So called ‘cold’ calling, where you just say “oh, I haven’t talked to X in forever, dialing” is generally a bad idea.
If there are no points of business to discuss, the phone call will become excessively difficult to maintain, even with a girl, if you have nothing important to talk about, you’ll just end up blathering on about a bunch of nonsense(or enduring awkward silence).
I think talking on the phone for over a half an hour is almost always a waste of time, unless there just so happens to be a lot of business to discuss, but even then, I prefer to just plan a meeting in person, or split the conversation into two different conversations.
Writing out some bulleted notes before making a call is a very smart thing to do, also having that same paper to take notes on can’t hurt.
Other than that, practice makes perfect. I’m a firm believer in not saying anything over the phone I wouldn’t say to that person face to face. likewise, don’t say something over email or text that you wouldn’t say over the phone.
I think a lot of times someone who thinks they are great face-to-face but can’t seem to translate that communicative energy to any other medium, is not really as good in person as they think they are.