As mentioned, you do need a compatible smartphone - iOS or Android - to use WhatsApp. Only then can it be used in a web browser, but everything still happens on the phone.
The problem is - WhatsApp requires a phone number, so you might be able to install Android x86 into a virtual machine on your computer. That might work assuming it doesn't start complaining about no SIM card being present. You can download the APK to install here if you don't wish to register for a Google Account for Google Play:
WhatsApp doesn't seem a professional tool for work purposes, you could suggest other tools built for business like Slack (free), Microsoft Teams, Google Hangouts (if using G Suite) or even stick to plain old e-mail.