What this tile shows
For a local business this is often the real conversion, and it never touches your website at all.
Squizzie calls this one Phone Calls. It reads as a single count.
Where the number comes from
Google Business Profile. Local search visibility, customer actions, search keywords, and reviews from Google Business Profile.
What you need for it to appear
A connected Google Business Profile location, through the same single Google sign-in.
The fuller picture
This is one figure out of a bigger subject. Search rankings and your local listing covers it properly.