Phobos (G5401) means fear, dread, or reverence — ranging from terrified fear before a great power to the reverent awe that is the beginning of wisdom. It gives English 'phobia.' The NT uses it both positively (the fear of God as reverential worship) and negatively (the paralyzing fear that perfect love casts out).
The 'fear of the LORD' (phobos Kuriou) is wisdom's foundation — carried directly from the Hebrew yirah (H3374) into the Greek NT. Acts 9:31 describes the early church walking 'in the fear of the Lord and in the comfort of the Holy Spirit.' 1 John 4:18 distinguishes: 'perfect love casts out fear (phobon)' — the tormented fear of judgment. The reconciled child of God no longer fears condemnation, yet grows in reverential awe before the holy Father.