Of everything on a Google Business Profile, the primary category is the field that does the most work and gets the least attention. It was set in ten minutes when the profile was created, usually by whoever happened to be at the keyboard, and it has not been looked at since.
Why it matters more than anything else
Google treats categories as the answer to "what is this business." When someone searches "pool builder Chandler," Google looks first for profiles whose primary category matches that intent. A pool company whose primary category is "Contractor" or "Landscaper" is not in that race, no matter how good the reviews are. The industry's annual ranking-factor survey puts the primary category at the top of the list, above everything else a business controls.
The two-minute check
Search for the exact thing you want to be found for, from a phone, from somewhere in your service area. Look at the three businesses in the map results. Open each one, scroll to the category line under the name. That is the category Google associates with that search. If yours is different, you have found the problem.
Common wrong answers in the trades
"Contractor" when you build pools. "Landscaper" when you do hardscape and never mow a lawn. "Construction Company" for a roofing contractor. "Home Improvement Store" for a remodeler, which happens more than you would think. Each of these puts the business in a broad, crowded category where it competes with everyone and matches nothing.
Secondary categories
Add them, up to nine, for the things you also do. A pool builder might carry "Swimming Pool Contractor" as primary and "Landscape Designer" and "Concrete Contractor" as secondary. Do not add categories for things you do not do; it dilutes the profile and Google notices.
What changing it does and does not do
Changing the primary category can trigger a re-verification. It is worth it. It will not fix reviews, completeness or distance, and it will not make the photos better. It will put the business in the right race, which is the precondition for everything else.
If you would rather someone else check, the free audit does exactly this against your three nearest competitors and sends back what we found.
Related: Visibility Setup · Free profile audit