How to get the phone number from a WhatsApp conversation in voiceflow.

Hi, I'm creating a chatbot where I want to give customers the ability to get their account information if I have their cell phone number registered in my database. My question is how can I obtain the WhatsApp number at the beginning of the conversation without requesting it from the user and when starting the flow. I would like to make a call to an API to validate if it is a client, if so, give a personalized welcome to the client, otherwise enter a generic flow.

I am currently using Voiceflow connected to Meta through Webhook (Replit) but if this is the most "simple" way to do it, I would create the webhook in a personal api. I have also tried using flowbridge.

I am open to any form of integration to obtain this.

Greetings to all