"They've sort of given him a 50/50 chance," he said.
"A young man just starting his life."
The plan is to try to wake him up on Monday, but the extent of damage to his brain and other organs remained uncertain, Phillips said.
Many of his bones are broken and there will be a lengthy recovery if he pulls through.
He said he bore no anger towards the driver, who he hoped would come forward voluntarily to the police.
"Accidents happen," he said.
"It's not like I've got anger or hate towards them."
Phillips said he wanted to thank the firefighters, St John staff and police who helped his son, his youngest boy, after he was hit, along with the hospital staff, for their exemplary care.
Ryan attended Verdon College in Invercargill and competed in Jiu-Jitsu.
Police said in a statement they want to hear from anyone travelling in the area at the time of the incident, as well as the driver and occupants of the vehicle involved.
Anyone with information is urged to contact the 105 line and quote file number 220925/5483.