Unfortunately, there is nothing you can do to prevent WhatsApp from sharing your phone number with Facebook. The messaging application announced that it would begin sharing its users' information with the social network on August 25, 2016, giving users until September 25 of that year to agree or disagree with the operation. What does this mean? In short, if you have installed WhatsApp on a new phone number, you cannot stop it.
However, there is something you can take advantage of by accessing Facebook through your mobile phone's web browser. It means that you cannot install the Facebook app (or its lite version) on your phone and therefore it will be more complicated to move around the WhatsApp interface, especially if we keep in mind that the applications were designed for mobile devices and in this case, you will have to use a web version focused on users with mouse and keyboard.
So, what is the point of doing it this way? The fact that Facebook will not be able to read your phone's data if it is not installed on it and you will get what you are looking for. Right now, this is the only way for applications not to communicate with each other; Facebook, WhatsApp, and Instagram are three apps developed by the same company and designed to exchange information between them, this implies that with the excuse of improving the user experience could (and will) share information between them.