You can keep it friendly by being clear once and then repeating it consistently. Next time you see them in the hall, give a quick heads-up rather than waiting for a knock: "Hey, I love our chats, but I'm on calls a lot and can't do drop-ins. Would you text before coming by? If I don't reply, assume I'm tied up." At the door, use a short broken-record script: "Hey! Bad timing—I'm on a call/winding down. Can you text me and we'll find a time?" Step out into the hallway and keep your body half-turned so it naturally stays brief, and offer a specific alternative: "I'm free Thursday after 6 if you want to catch up." If they keep talking, repeat once: "I've got to get back to it—text me and we'll plan something."
Give yourself some small, non-passive-aggressive signals and tech help.
Put a small label by the bell: "Neighbors/friends: please text before knocking. Deliveries/maintenance: ring bell." A simple flip sign or door hanger during work hours—"On calls, please text first" on one side and "Free to chat" on the other—lets you be consistent. If you have a smart doorbell, set quiet hours/Do Not Disturb during work time and use the two-way audio to accept packages but decline chats; if not, use the peephole or a door chain to screen quickly without fully opening. You can also mention a standing boundary in conversation: "Weekdays 9–5 I'm not answering the door unless it's a delivery." If they continue dropping by unannounced after all that, be direct but warm: "I really need you to text before stopping by; if there's no text, I probably won't answer."