The Presiding Officer is majority-party Senator who presides over the United States Senate and is charged with maintaining order and decorum, recognizing Members to speak, and interpreting the Senate's rules, practices and precedents.

There is no actual office of "Presiding Officer". Whoever is presiding is the Presiding Officer. That can be the President of the Senate (the United States Vice President), the President Pro Tempore, or someone designated by the President Pro Tempore. Typically, a junior senator presides.

Source

• Senate.gov

Employees of the United States Congress | United States Senate