The Phobians announced the signing of the former Ghana midfielder in a Twitter post on Tuesday afternoon.
Muntari had been training with the Phobians, which sparked talks of a possible transfer to the Accra-based side.
In a post on Twitter, Hearts shared a video of the midfielder along with the caption: “Welcome to Hearts of Oak.”
Muntari started his career with Ghana Premier League side Liberty Professionals before moving abroad.
He has since lined up for the likes of AC Milan, Sunderland, Pescara, Deportivo La Coruna and Inter Milan, where he won the Champions League.
The 37-year-old has, however, been inactive for over two years after parting ways with Spanish side Albacete in the summer of 2019.
Hearts would hope that the signing of the experienced midfielder would help the club in its bid to retain the league title.
The Phobians currently sit in fifth position and trail rivals Asante Kotoko by 10 points after 14 rounds of matches.
Source: Dominic Of Newsanchorhub