This code worked for me.
After clicking on the link, it will ask you to choose the contact to share a message.
<a href="https://api.whatsapp.com/send?text=enter message here">Click here to share on Whatsapp</a>
_x000D_
You can add target="_blank" attribute to open it in a new window or tab.
I don't think the phone number is needed when someone wants to share a particular message or article.