Why won't a phone selfie do? It's easy, it's there, why should you take the time to get dressed up and hire someone?
Interacting with a phone isn't the same as interacting with a person and it shows in the photos. You want your headshot to be open, friendly and inviting, laughing or smiling with authentic feeling.
Add in professional lighting, full retouching, and 20 years of photo experience... the difference is clear!