The hostage-taking raised questions in the US about how to combat piracy and whether suspects could be tried in US courts.
Robert Gates, the US defence secretary, said on Monday there was "no purely military solution" to the problem of piracy, according to a report by the US military news service.
Gates said Phillips's captors were 17-19 years old, "untrained teenagers with heavy weapons", drawn to piracy by a lack of economic alternatives.
"As long as you've got this incredible number of poor people and the risks are relatively small, there's really no way in my view to control it unless you get something on land that begins to change the equation for these kids."
Hijackings are an ongoing problem in the busy shipping lanes off the coast of Somalia.
At least a dozen ships have been seized in the Indian ocean and more than 200 crew members are being held hostage.
The pirates had attacked the US-flagged Maersk Alabama container ship before taking Phillips hostage with them on a lifeboat.
|Richard Phillips was rescued after US navy snipers killed three of his captors [Reuters]
He reportedly jumped from the vessel in an attempt to escape, but was quickly re-captured.
Two US navy warships were sent to the scene to monitor the situation and rescue Phillips, a plan approved by Obama.
The US navy said the snipers opened fire when Phillips's life appeared to be in danger.
But a Somali pirate leader told the AFP news agency that US forces had shot and killed the men, even after they had agreed to free the hostage.
Before the raid, the pirates, who had demanded a $2m ransom for Phillips, warned the US government not to use force.
The raid occurred only two days after French commandos stormed a yacht to rescue two French couples and a child being held by Somali pirates in a separate incident.
That raid left one of the hostages and two pirates dead.