What is the highest us clinical development phase reached by the drug aklief?

What clinical phase did Aklief (trifarotene) reach in the U.S.?

Aklief (trifarotene) reached Phase 3 in U.S. clinical development [1].

Where does that place Aklief in the overall U.S. development timeline?

Reaching Phase 3 is typically the late-stage step used to support regulatory review and labeling decisions, and trifarotene is approved in the U.S. for its indicated uses after those Phase 3 studies [1].

Sources
[1] https://www.drugpatentwatch.com/patent/aklief