Hi all
a couple of points:
1) Round and sphere are not synonyms, the ancients (virtually?) all believed the earth was round, they did not believe it was a sphere. They viewed it as a flat disk some cultures had elaborate systems in place such as a disk on the back of an elephent or turtle.
2) The above is true for the “hamon Am” the intelligentsia knew for thousands of years that the earth is spherical. There is much observational evidence for the spherical shape of earth including ships going over the horizon, lunar eclipses, and careful mapping of the sun/stars in different positions. In fact not only did Ancient Greek philosphers accept a spherical earth, but in 240 B.C.E Eratosthenes calculated the circumference with decent precision
3) The yerushalmi does not necessarily mean the Earth is shaped like a ball. Clearly, “es hayam Kekarah” does not fit with the Earth as we observe it. Some rishonim understood it to mean that the deity was in control of the earth “like a ball” i.e. like one controls a ball,not that that was the shape. Similar to makal which clearly isnt referring to shape. Rabbeinu chanalel says this clearly, Pnei Moshe is also mashma like this.