Despite this being a female to male transformation audio. There is nothing mature or NSFW in it. The only hint to the gender change is when she exclaims about her chest. You can let your imagination run wild with how that happens.

In this audio, a girl is playing Pokémon Go on her phone. She catches a Machoke and checks out its Pokedex entry. She then noticed a circler button appear at the bottom left. She presses it only for her phone to shock her. When trying to pick up her phone, she starts evolving into something, muscular.

Sound effects from youtube, freesound, Pokémon games/anime, and LizSFX2016