I think it's both. If I recall correctly, Form (μορφή, "morphe") has meaning in Greek philosophy in regards to a thing's nature, i.e. everything is an implementation of Form and Substance. But the contrast between verse 6 and 7 is between "God" and "Slave", which goes beyond nature and includes demeanor, i.e. God owns everything and commands all, while a slave owns nothing and serves all. So, I think you're on to something.
The form of a servant (morphēn doulou). He took the characteristic attributes (morphēn as in Php_2:6) of a slave. His humanity was as real as his deity.
In the likeness of men (en homoiōmati anthrōpōn). It was a likeness, but a real likeness (Kennedy), no mere phantom humanity as the Docetic Gnostics held. Note the difference in tense between huparchōn (eternal existence in the morphē of God) and genomenos (second aorist middle participle of ginomai, becoming, definite entrance in time upon his humanity).
Robertson.
The same word for form as in the phrase form of God, and with the same sense. The mode of expression of a slave's being is indeed apprehensible, and is associated with human shape, but it is not this side of the fact which Paul is developing. It is that Christ assumed that mode of being which answered to, and was the complete and characteristic expression of, the slave's being. The mode itself is not defined. This is appropriately inserted here as bringing out the contrast with counted not equality with God, etc. What Christ grasped at in His incarnation was not divine sovereignty, but service.
Was made in the likeness of men (ἐν ὁμοιώματι ἀνθρώπων γενόμενος)
Lit., becoming in, etc. Notice the choice of the verb, not was, but became: entered into a new state. Likeness. The word does not imply the reality of our Lord's humanity, μορφή form implied the reality of His deity. That fact is stated in the form of a servant. Neither is εἰκών image employed, which, for our purposes, implies substantially the same as μορφή. See on Col_1:15. As form of a servant exhibits the inmost reality of Christ's condition as a servant - that He became really and essentially the servant of men (Luk_22:27) - so likeness of men expresses the fact that His mode of manifestation resembled what men are. This leaves room for the assumption of another side of His nature - the divine - in the likeness of which He did not appear. As He appealed to men, He was like themselves, with a real likeness; but this likeness to men did not express His whole self. The totality of His being could not appear to men, for that involved the form of God. Hence the apostle views Him solely as He could appear to men. All that was possible was a real and complete likeness to humanity. What He was essentially and eternally could not enter into His human mode of existence. Humanly He was like men, but regarded with reference to His whole self, He was not identical with man, because there was an element of His personality which did not dwell in them - equality with God. Hence the statement of His human manifestation is necessarily limited by this fact, and is confined to likeness and does not extend to identity. “To affirm likeness is at once to assert similarity and to deny sameness” (Dickson). See on Rom_8:3.
Vincent
Is this correct?
J.