Yes, ma’am. Should we start by defining voice? And we ought to talk a little about critiquing groups and editors, too. Editors ≠ CPs!
Okay, I'll start. Voice is the unique way through words this piece of writing expresses a worldview, attitude, mood, tone, and purpose.
What's important here is it's the way a piece of writing expresses all those. That is, I don't think "voice" is necessarily an authorial-exclusive entity. Many authors vary their voices from story to story. Many write through the voices of their characters.
But anyway, I think voice has much more going on than diction (word choice). Worldview, for example. There are books where the worldview is profoundly pessismistic (dystopias, for example), and that comes through in the voice. If it's a comedy, it will be a dark comedy, full of grimmer terminology and gallows humor, not a light romp full of slapstick and gentle humor.
I don't believe this voice thing is entirely conscious, but I definitely think you can rationally revise to refine your voice. I also think that a few moments of focus before you write can help you generate the voice if it doesn't come out as you write.
That is, if you feel that your story is "voice-less" or bland, next time before you start to write, sit down and close your eyes and imaginatively immerse yourself in the world of the book. Envision a couple scenes; slide into the consciousness of the main character. Start to write with the feeling of the book looming over you.
Also try this: Put on music that "feels" like the book.
My son has been writing a romantic comedy screenplay, and he said he's listened to Bruce Springsteen's new song "Girls in Their Summer Clothes" on "repeat" for weeks now as he writes. He says the buoyancy of the melody and the romantic lyrics make the dialogue and emotion flow better.