What is the basic difference between a Pharisee & a Sadducee in regards to Torah & the Oral Law

The Sadducees, like the Karaites who came after them, did not accept the Oral Law while the Pharisees did.

Would it be fair to say that the Sadducees took a more “letter of the Law” approach while the Pharisees took a more “spirit of the Law’ approach ?

No, I do not think that would be accurate. There are many laws in the written Torah that would totally confuse us if we did not have the Oral Law to elaborate. For example, the Torah states that these words shall be “totafot” between your eyes (Deuteronomy 6:8). The word, “Totafot”, is a new term and we would not know what G’d intended. Perhaps He meant for us to daub colored clay between our eyes as the Hindus do. The Oral Law clarifies what “Totafot” are and, amazingly, everywhere in the world that Jews have ever lived, the Tefillin (phylacteries) that they wear on their foreheads between the eyes are the same.

The Oral Law, therefore, does not change the Written Law, it clarifies it. But we are still obeying the “letter of the law” which is to place a physical sign between one’s eyes. “Spirit of the Law” would suggest a metaphysical interpretation such as “thinking about G’d” instead of a concrete placing of a physical object between one’s eyes.