How to track a link on an external website through HubSpot


We are working on a website that is developed in a custom CMS called NetDirector by GForces.

We are about to launch a PPC campaign using the Ads add-on on HubSpot (Pro License) but we are trying to figure out conversion tracking.
Currently, there are some trackable links inserted inside specific sections of the website (e.g. the contact page with all the phone numbers), and we have been tracking the clicks on those links to report back on “leads” generated from the PPC campaign.

Is something like this possible in HubSpot at all?

I know we can track conversions based on form submissions, but in this particular case, there is a much higher likelihood that someone will call rather than fill out a form, and because there is no call tracking app on the website, we really need to be tracking how many people have clicked the link to call us.