What is a word or phrase that describes "a person who is having difficulty speaking with girls?"
I've seen in various old books (Vanity Fair, if I rightly recall) such a person described as a hobbledehoy, meaning an awkward, tongue-tied young man.
In psychology, Parthenophobia refers to an abnormal and persistent fear of virgins or young girls.
How about "selective mutist", a selective mutist is someone who cannot talk in certain conditions, but is quite chatty in others. For instance, a boy at school having difficulty chatting with other girls, but when he gets home, jokes around a lot with his sister.
If that wasn't clear enough, how about "parthenophobic selective mutist"....
I would say Coy is related especially to Bashful/Shy - by not necessarily when talking to girls