You ask a very good question that I used to ponder. In fact, for a long time I believed that it was impossible to give remote readings and was probably a scam. But as my psychic abilities have progressed I now have a better understanding of how a remote reading works.
There are some psychics who require that their clients be face to face with them in order to give accurate readings. But I am actually finding that this is the exception more than the rule. I find that most psychics give very good readings remotely. The reason for this is that the ability to connect spiritually to someone is kind of like how the internet works. If you have a friend email you a document that you've been waiting on, you're going to need a computer or mobile device plus an internet connection in order to retireve your friend's email. If the power is out in your neighborhood, you're not going to be able to use your equipment to retrieve that email. But if the power is up, and your internet provider is up, you'll have no problem receiving that email. Similarly, being psychic is like having a spiritual internet connection that the average person doesn't have access to (the power is on for a psychic). We have a built in spiritual modem in our brains that allow us to access this spiritual internet. And as a result, the majority of psychics do not need to see you in person to do a reading. Just speaking with you by phone allows them to connect with your spirit through the spiritual internet and access info. that you are seeking.
I wanted to note in helping you understand this that I actually get tripped up doing readings face to face with people. In person my mind gets a little confused analyzing someone's facial cues and behavior while also accessing that person's spirit. I get mixed messages. For that reason, I am more accurate via email or on the phone with someone where I don't have anything visual to confuse me.