Phil is opening a new gym and wants an expert to design his logo. which file format would the developer use to save the artwork?

A vector format, such as postscript or svg!

Vector formats do not use pixels and therefore can be scaled and zoomed without ever becoming pixelated. Note that when the logo is actually used (e.g., on a web-site), it will typically be rendered as a bitmap (e.g., PNG image) of a certain size (number of pixels).