The 31-year-old came to Brazil as the most decorated Olympian in history and has now won 23 medals at five Games.
But how does the American’s tally compare to current Olympic countries?
Phelps on the all-time Olympic medal table
A selected all-time medal table shows Phelps in joint 35th position, ahead of the likes of India, which has a population of over 1.2 billion.
Great Britain’s own leading Olympic gold medal-winner, cyclist Sir Chris Hoy, has six to his name, which leaves him joint 50th in the table along with Indonesia, Croatia, Azerbaijan, Georgia, Morocco and Lithuania.
Phelps’ haul on the global map
There are 206 countries with delegates competing in the 2016 Rio Olympics.
Phelps has more gold medals than 170 of those countries – more than 65%.
Greenland and Western Sahara are both grey on this map as they are not currently Olympic countries.