at the bottom of the ladder
Occupying the lowest, most basic position in a given group. Quarks are at the bottom of the ladder in the physical makeup of matter. Tech startups may start at the bottom of the ladder economically, but, given their business model, they have a very high potential for growth.
at the bottom of the ladder
and on the bottom rung (of the ladder)Fig. at the lowest level of pay and status. (Alludes to the lowness of the bottom rung of a ladder.) Most people start work at the bottom of the ladder. After Ann got fired, she had to start all over again on the bottom rung.