This is another term like social anxiety used by teens anytime they have to do something they don't like or go somewhere they don't want to go. Shrinks use these terms, but they have to make a living.
They are not real diseases (like anxiety and phobias) and the cause is almost always the same thing: too much time on electronics and not enough time interacting with real humans in real life situations. The teens on here will eat me alive, but I'm an adult who counsels older teens and young adults. I know what I've seen.
If this is possible, you've got to find a better way to limit phone interactions and REQUIRE more activities, whether they're school based or something else, like community based. There are lots of online recommendations for limiting phone use, the biggest being never let a teen take a phone to bed with them. Also, I hope and assume you're monitoring her activities on that phone.
The more she gets out and about, especially with activities where there's shared interest (sports, music) the quicker she'll adapt. She may be shy and this won't change, but shy people are perfectly functional.