Where it goes
Top of every page, in the header, plus once more near the bottom where somebody who read the whole thing ends up. Not only on the contact page. The visitor who's ready to call is rarely on the page you expected them to be on.
Make it real text rather than part of a picture, and make it a tap-to-call link. A number inside an image can't be tapped, can't be copied, and can't be read by anything but a person squinting at it.
Why it has to match your listing
Search engines line up businesses across the web by the name, address and phone number they find. When those agree everywhere, it's easy. When your site says one number and your Google listing says another, it's two businesses as far as a machine can tell.
This matters most for a business that's new or not well known, which is most contractors. It's a one time cleanup, not a monthly service, and anybody selling it as a monthly service is selling you an afternoon of work over and over.
Tracking numbers, carefully
A tracking number that shows which ad brought a call is useful, and it's fine to use one. The safe way is to keep your real number as the one on your Google listing and in the code behind your site, and swap the displayed number for paid traffic only.
What causes trouble is putting a tracking number on the listing, or a different one on every page of the site, so nothing matches anything. If you can't keep it straight, use one number everywhere and count leads a different way.
What else belongs beside it
The towns you serve, in words, and your hours. Somebody standing in a driveway in the next town wants to know you come there before they dial, and a page that doesn't say leaves them guessing. Hours matter for the same reason: somebody deciding at seven in the evening wants to know whether calling now is worth it.
A form is worth having next to the number, not instead of it. Some people won't call a stranger and will type. Some won't type and will call. Offering both costs you nothing and catches both, and the form gives you the address and the job in writing before you ring back.