What is phi in probit model?

Could you please explain what phi represents in the context of a probit model? I'm curious to understand its significance and how it's used in this type of statistical analysis. I'm aware that probit models are commonly employed in econometrics and finance, but I'm not entirely clear on the role that phi plays within these models. Could you elaborate on this concept in a way that's easy to comprehend for someone who's new to the field?