Basements, boiler rooms and freight elevators are where your site really loads
Your page is being opened in the worst signal conditions in the building, and speed stops being a technical metric at that point.
The visitor is rarely at a desk. They are in a cellar looking at a boiler, in a stairwell, in an elevator lobby, or standing over a floor drain in a basement laundry room. Signal in those places is poor and patience is shorter than usual.
Test on a throttled connection, not on the office network. A page that feels instant on fiber can take long enough on a weak signal that the visitor backs out and calls whoever loaded first.
The usual culprits are predictable. Oversized hero images, a video nobody watches, a chat widget, three tracking scripts and a review carousel that pulls from somewhere else. Each one is a delay you are choosing.
Keep the phone number in markup that renders before anything else. If everything below the fold fails to load, the visitor should still be able to place a call.