Lead calls phone number on landing page, website, ad, etc... the call is automatically forwarded to your client, with no need for your intervention. Many times it also records the calls so you can verify if a lead is good or not. They attempt to close the deal. You're sending them a lead from someone looking to do business with them since your landing page is about their business.
Some call tracking programs have even more advanced features like forwarding to multiple clients or employees of your client since many call tracking programs have round robin systems and systems if one doesn't answer it moves onto the next number.
With email sometimes you'll get a good return email, sometimes typos, sometimes no phone number, sometimes tire kickers... There can be tire kickers on phone calls also but they're reaching out and you have time to tell them the value you offer in that phone call immediately. With an email you have to email back if there is no phone number. There may be a long back and forth, the client may never respond back, your email gets caught in spam....
There is more value in a phone call. If you can charge them for both, even better.
An example of pricing would be a phone call lead is worth $60 an email lead is worth $15. This varies by niche but usually there is a big price differential.