Sulfur is located below oxygen in Group 16 (also known as the oxygen family) of the periodic table. As we move down a group in the periodic table, the atomic radius increases, and the ionization energy decreases. This means that the valence electrons in sulfur are more loosely held and are more easily removed, making sulfur more reactive than oxygen.

In contrast, phosphorus is located below sulfur in Group 15 (also known as the nitrogen family) of the periodic table. Phosphorus has a smaller atomic radius and higher ionization energy than sulfur. This means that the valence electrons in phosphorus are more tightly held and are not as easily removed, making phosphorus less reactive than sulfur.

The reactivity of sulfur is also influenced by its lower electronegativity compared to phosphorus. Electronegativity is the ability of an atom to attract electrons. The lower electronegativity of sulfur means that it has a weaker attraction for electrons, making it more likely to lose electrons and undergo chemical reactions.

Therefore, based on the position in the periodic table, atomic properties, and electronegativity, sulfur is more reactive than phosphorus.