The list of disadvantages to phone readings is a short one. There’s the fact that you can’t see the person you’re talking to - that seems to be a major disadvantage for some. You also don’t have the atmosphere that you have when you personally visit a psychic. Finally, there’s always the chance that you end up with someone on the phone who stalls just to make time on the phone (which racks up a bigger bill for you).
This was a lot more common in the early 1990s and 2000s when phone psychic readings were still new. It’s not as common a practice anymore, but it’s still out there and something to watch out for.