Why are there 3 different types of call tracking (Calls from ads using call extensions or call-only ads, Calls to a phone number on your website, Clicks on your number on your mobile website)?

The two that are confusing to me are the mobile vs calls to a phone number on your website - shouldn’t those be the same?

If someone on a mobile device clicked on the ad and called, would it be tracked using the “Calls to a phone number on your website” tracking code?

And do I need to set up conv tracking for both?

Thanks,

Austin