The lunch hour is where a small shop quietly drops calls
Pull the phone report by hour and day before you change anything else, because the gap is almost never where the owner thinks it is.
Count unanswered calls, abandoned holds and voicemails by hour for the last ninety days. In most small shops the pattern is the same: midday, shift change, and the first hour after the office closes.
The fix is rarely a new phone system. Overflow to a second phone, a briefed answering service that knows your service area and your fee, or a rule that whoever is not on a call picks up on the second ring will move the number.
Whoever answers needs the service area and the refusal script in front of them. An answering service that books a job in a town you do not serve has cost you more than the missed call would have.
Report answer rate weekly and put it on the wall. It is the one conversion metric a plumbing business can move this week without touching the website.