Foremost and High up

Foremost adjective - Coming before all others in importance.

High up and foremost are semantically related In some cases you can replace phrase "High up" with "Foremost", this terms are similar.

High up adverb - At a great altitude.

Foremost and high up are semantically related in eminent topic. Sometimes you can use "Foremost" instead an adjective phrase "High up", if it concerns topics such as chief, high-ranking.