As for the mention of Hebrews 5:8 (that relates to Philippians 2:8 and Hebrews 2:10):
Well, before Christ came down into the flesh of a man, He did not suffer in doing the Father's will. Hebrews 5:8 says He learned to be obedient by the things which he suffered. Does this mean Jesus was disobedient to the Father at any point? No. John 8:29 says Jesus always did what pleases the Father. Jesus was without sin, and he was holy, undefiled, and separate from sinners (Hebrews 4:15) (Hebrews 7:26), (Hebrews 9:14).
Christ went from "Obedience to God that was not tested" (by the devil and man) before the Incarnation and He went into the realm of being of "Obedience to God that was tested" while as a man (Who was under the curse of suffering) so as to suffer in our place.
Jesus learned obedience experientially (i.e. thru experience) in man's suffering of the curse of the fall (See Genesis 3). Jesus was being our substitute. He took on our sin that came from Adam (and the suffering thereof) in order to be the author of our salvation, which was made complete (or perfect) thru the suffering he experienced. In other words, the penalty or price for sin could not be paid in it's entirety without the Lord experiencing the suffering (that is both the result and curse of sin from the beginning). God the Father could not have laid Judgment against sin that Jesus took on within His body on our behalf (With the taking of the cup in the Garden) while He was on the cross if He did not suffer the consequences of sin.
Hebrews 2:10 NIV
"In bringing many sons to glory, it was fitting that God, for whom and through whom everything exists, should make the author of their salvation perfect [made complete] through suffering."