Yes, Jesus was a spiritual being before God changed him into human form.
As I understand it, Jesus existed with God before the universe was created. The whole universe, and all physical life on earth, was created by Jesus as directed by God. Even all the heavenly spirit beings - angels, cherubim and seraphim - were also created by Jesus. So Jesus could not have been a physical being at that time (physical matter had yet to be created), and therefore he could only have been a spiritual being.
Colossians 1 (WEB):
(16) For by him all things were created, in the heavens and on the earth, things visible and things invisible, whether thrones or dominions or principalities or powers; all things have been created through him, and for him.
(17) He is before all things, and in him all things are held together.
Revelation 3:14 (TLV):
(14) To the angel of Messiah’s community in Laodicea write: “Thus says the Amen, the Faithful and True Witness, the Originator of God’s creation:
Jesus is now a spirit being again, and Christians are promised, as members of Christ's body, that they will have the same nature as Jesus now has - the divine nature - the highest form of spirit being, having immortality:
John 4:24 (WEB): God is spirit, and those who worship him must worship in spirit and truth.
John 17:5 (WEB): Now, Father, glorify me with your own self with the glory which I had with you before the world existed.
(God more than answered that prayer, granting him the immortal divine nature - previously he was mortal.)
2 Peter 1:4 (WEB): ... he has granted to us his precious and exceedingly great promises; that through these you may become partakers of the divine nature.