Thanks for your question.
Although both the Prime Minister and the Speaker are members of the House of Representatives, it is not possible for the same person to do both jobs. The positions are quite different, and each has many responsibilities.
The Prime Minister is the leader of the Australian Government and their position includes:
The Speaker also has many responsibilities, including:
Unlike the Prime Minister, the Speaker does not usually give speeches and participate in debates in the House of Representatives and only votes if there is a tie.