E.P. Sanders was a senior biblical scholar who had a huge impact on the field of study. His comments on Phil 2.5–11 are to the point.
In any case, “equality with,” like “form of,” avoids direct identification of Christ with God. The New Testament authors had not yet thought of the idea of the Trinity, and so making Christ a part of a larger Godhead was not an option. His precise relationship no God was usually just called "sonship," which could have a broad meaning as we shall see when we discuss Romans 1. All Israelites were in some sense "sons of God."
In later years, Paul's use of "form of God" and "being found in human form," would lead to numerous debates: was he God or human merely in appearance? In particular, was he a real human? Fortunately we do not have to delve into this. The hymn as written uses "form of" to mean "possessed at least some of the characteristics of," not merely "appeared to be." On the other hand, "possessed at least some of the characteristics of" proposes less identity between God and Jesus than is expressed in the much later formulation, that God and Christ were of the same ousia, "essence."E. P. Sanders, (2016). Paul: The apostle's life, letters and thought. scm Press, p 603