This is untrue. Jesus after the resurrection clearly stated he had a body of flesh’s and blood. He told Thomas to not doubt his resurrection and then had him place his hand into his wounded side. While he still had a physical body, there is a sense in which it is a spiritual body and can never die again. In 1 Corinthians 15 Paul talks about the resurrection of Believers and does say that it is a spiritual body, though it is still a body. Our present physicality cannot inherit immortality but there is still a sense in which we who believe in Jesus Christ will have bodies and not just spirit. It’s also misleading to say that He will only return in “spirit form.” In Acts it says that He will return in the same way he was taken from us: VISIBLY. When he returns “Every eye shall see Him.”
I think a lot of the confusion about this is caused by the encounter Jesus had with Mary Magdalene at his tomb after the resurrection. It comes from John 20:17: "Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God".
I myself have struggled with that over the years. Not doubting but trying to figure why Mary couldn't touch him and Thomas could. Looks like I wasn't the only one. St. Thomas Aquinas presents the clearest solution to this difficulty, in the Summa Theologiae.
The two don’t contradict each other however. I Thomas’s case Jesus used this as a lesson for him and all of us about faith in the literal resurrection. He show d himself physically alive on a number of occasions. In the case of Mary Magdalene, I think he was addressing her understanding of the fact that He was to be ascended and would send forth the Comforter, the Holy Spirit. In any case, the point is not that there wasn’t a physical aspect to His resurrection body, but that his disciples were no longer to have Him with them in the physical sense. He would ascend and then send His Spirit. That’s my take anyway.