accounts on iCloud

If you want to separate your private and business phone

then you should use a 2 different Apple ID and of course you'll have another iCloud address/account

Example, private

your-name@example.com (Apple ID)

your-name@icloud.com (alias)

Example, business

your-biz@biz.com (Apple ID)

your-biz@icloud.com (Alias)

To make it simple use the same password for both accounts (but don't use simple password)

No.

iCloud is an alias to your Apple ID.

You can only use one Apple ID on your iPhone.