A contact not showing in my phone but in WhatsApp

I wanted to delete a contact from my phone, but to my surprise, when I searched for their name in my phone's contacts, nothing showed up. No one with that name or number was in my contact list. Their name, profile picture, status, etc. are all showing normally on WhatsApp and Telegram though. I tried to clear the cache for WhatsApp and also refreshed the contact list. Nothing changed. I was curious and checked a few other contacts that I saved through WhatsApp. They don't show up in my phone's contacts either. So I have their number but somehow cannot delete them. Does anyone know what to do here?