Hebrews 5:7:
7 Who in the days of his flesh, when he had offered up prayers and supplications with strong crying and tears unto him that was able to save him from death, and was heard in that he feared; [KJV]
7 who in the days of his flesh both prayers and supplications unto Him who was able to save him from death -- with strong crying and tears -- having offered up, and having been heard in respect to that which he feared, [YLT]
7 In the days of his flesh, Jesus offered up prayers and supplications, with loud cries and tears, to him who was able to save him from death, and he was heard because of his reverence. [ESV]
For me, the phrase "the days of his flesh" has the implication that Jesus, at some point, had a fleshless form of existence. The question is: when? We have two options: either (1) prior to his birth or (2) after his death and resurrection. In order to decide between the two, let's consider the light shed by Luke 24:39 (ESV):
39 See my hands and my feet, that it is I myself. Touch me, and see. For a spirit does not have flesh and bones as you see that I have.”
Luke 24:39 is telling us that, after his resurrection, Jesus was still in the flesh, or at least that he still retained his physical body of flesh and bones. Does this mean that we should rule out option (2) in favor of option (1): that Jesus had a fleshless pre-existence?