What are their intentions?

So I have a compilation channel and I often receive similar kind of emails on my email id (that I have attached to my youtube account for promotional purposes).

The emails usually starts with "they want to work with me, advertise on my channel etc".... And at the end of the email, every single one of them want me to contact them on whatsapp. They mention in the email that they would love to talk on whatsapp.... It tells me that they are trying to get my number somehow? For what reason? Is this some kind of phishing technique?

Why not use another number not related to you or your channel and chat them up?
Or you can clearly say that you don't like chatting on Whatsapp and want the discussion to be carried out via email only.

It's just a theory, but they are trying to get your mobile phone number, to clone it so they can access your account. Don't do that.

Ask them to email communication for business enquiries