Two older teenagers attacked him from behind, knocking him to the ground and kicking him in the face.
Darragh's mother Paula today told the Herald her son was left shaken and bloodied by the terrifying ordeal.
"They were brutal with my son," the mother-of-five said. "It was horrific. It was just disgraceful. Darragh was very shaken up."
The teenager, a pupil at Old Bawn Community School in Tallaght, was walking through Sean Walsh Memorial Park when two older youths passed him.
"When they saw he was on the phone, they stopped and turned back. They started to beat him. He wouldn't give them his phone.
"They thought he would just hand it over. He was on the ground. They pushed his head into the grass and they were kicking him. It was really upsetting. I've been completely upset about it," his mother Paula said.
"They were brutal with my son," added the mum-of-five.
Paula (40) said her son -- who does boxing in St Mary's Boxing Club in Tallaght -- is not an easy target and was upset at not being able to get his phone back from the thugs.
As they made off, Darragh went after them but he wasn't able to catch the pair.
She said the whole community is talking about the anti-social behaviour which goes on in the park, close to the popular The Square Shopping Centre.
When she took Darragh to the doctor after the attack, a woman in the surgery told her about an assault on her own daughter, Paula said.
The park was developed for the people of Tallaght but "it seems to have been taken over by these lunatics", Paula said.
The thugs attacked Darragh from behind so he could not defend himself in the incident last Friday week.
Paula added that she is going to approach local TDs Brian Hayes (Fine Gael) and Sean Crowe (Sinn Fein) to see what is being done about the public safety problems.
"Why should we be afraid there? It (the park) was purpose built for us to enjoy. At 2pm, you think you're okay."
A garda spokesman confirmed they received a complaint of a robbery from the person at Sean Walsh Park on November 23.
Two youths were detained and interviewed. They were released and a file is being prepared for the Director of Public Prosecutions.