A person at the front desk
A receptionist on your payroll learns the business: the regular customers, the crew, which jobs tend to run late. They can walk out to the yard to find someone and look after a customer at the counter. The limit is one person. They take one call at a time, need breaks and leave, and the role has to be filled again when they move on. If customers walk in, or the office work needs someone on site, a staff receptionist is often still the right call.