When consciousness (in a word, reflective cognizance) exists in this plane--which means only that it is in this mental frequency as opposed to 30 alternate ranges--then it generates gross matter or collects gross matter to form the body by the kammic processes. When the mental frequency of this consciousness is altered there is the generation of a mental form body, constructed of 'fine-matter' as is generated in the Form realm (Brahma planes). If consciousness is in the form-body then it is still in the material body, a form-body has simply been constructed from the mind which arose with no form-body at the beginning of that life (this is apparently what astral-projection is in reality). In this way there is traveling to the planes of the Form-realm, but only in the sense that one has consciousness and faculties there.
In the Pali Canon it is illustrated that the Buddha ascended
to Tavatimsa to deliver the Abhidhamma to all the devas who assembled there, and he descended
each day to eat material food which his body
yet required. This describes his material body not being perceived in this plane, as though it becomes more subtle as the beings on that plane with the adjustment of his mental frequency. This is how travel to the other 10 planes in the Sensual realm is, because it matter is generated in these frequencies. In the Form realm, fine-matter is generated and to be in that realm is to have a fine-material body--it is impossible for MATTER to be present in a frequency of FINE-MATTER, and likewise NO-MATTER as in the Formless realm. Remember that consciousness is simply the reflective cognizance of whatever the body is experiencing
(sensations, perceptions, mental formations).
The controversy here on this page really concerns the body that exists on different planes. The solution is that the Abhidhamma illustrates material bodies in the Sensual realm (any of the first 11 planes), and fine-material bodies in the Form realm (12-27). Moving to another plane does not mean taking gross matter and shoving it through some spatial membrane
--that's materialistic 'delusionism'
--but it means simply that the mental frequency is altered to be congruent of those beings existing on that plane, and a body (or formless consciousness) generated in that plane