Based on who's definition? Plenty of people use "middle management" to describe anyone under executives, but who doesn't spend time closely aligned with front-line work. In some structures, lowest level management is closely integrated with front-line, but I'd argue PHB has next to zero exposure to the actual work or goings-on.
PHB is Dilbert’s boss, yes? That’s front line manager, first level manager, whatever. By definition a middle manager has managers above and below them.
No. A first level manager cannot be middle management. A small company might not have middle management but the first level manager is bottom management.
