Ephesians 1:3-12
3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us with every spiritual blessing in the heavenly places in Christ, 4 just as He chose us in Him before the foundation of the world, that we should be holy and blameless before Him. In love 5 He predestined us to adoption as sons through Jesus Christ to Himself, according to the kind intention of His will, 6 to the praise of the glory of His grace, which He freely bestowed on us in the Beloved. 7 In Him we have redemption through His blood, the forgiveness of our trespasses, according to the riches of His grace, 8 which He lavished upon us. In all wisdom and insight 9 He made known to us the mystery of His will, according to His kind intention which He purposed in Him 10 with a view to an administration suitable to the fulness of the times, that is, the summing up of all things in Christ, things in the heavens and things upon the earth. In Him 11 also we have obtained an inheritance, having been predestined according to His purpose who works all things after the counsel of His will, 12 to the end that we who were the first to hope in Christ should be to the praise of His glory. NAS
All believers who are saved by (or through) grace through faith in Jesus Christ can be viewed as "preexisting" in God's mind. This is based on God's foreknowledge (Romans 8:28) or omniscience.
Peter said in Acts 2:
Acts 2:23 this Man, delivered up by the predetermined plan and foreknowledge of God, you nailed to a cross by the hands of godless men and put Him to death. NAS
Now all that God spoke (used words or logos) into existence by the words He used existed in the beginning with Him and express His ominiscience, which includes His predetermined plans. Jesus who was born of a woman in both space and time is the fulfillment of God's planned redemption of those who have faith in God and God's plan. Therefore Jesus preexisted in the mind of God not as an eternal divine entity.