London (CNN) -- Former tabloid editor and ex-Downing Street communications chief Andy Coulson was sentenced Friday in London to 18 months in prison for phone hacking offenses.
Coulson, who was editor of News of the World from 2003 to 2007, was convicted last week at the Old Bailey court of conspiracy to hack phones between 2000 and 2006. He had denied the charge.
He could have been given up to two years in prison.
Handing down sentences to Coulson and four of his former colleagues at the newspaper, owned by media baron Rupert Murdoch's News Corp., Judge John Saunders said the Prime Minister's ex-aide had to face the heaviest penalty.
"There is insufficient evidence to conclude that he started the phone hacking, but there is ample evidence that it increased enormously while he was the editor," he said.
"On the jury's verdict he knew about it and encouraged it when he should have stopped it. It was his reputation as an editor and journalist, which was increased through the stories that were obtained by phone hacking and, even though he resigned, he did so with his reputation intact."
Coulson's former colleagues pleaded guilty to phone hacking charges before the case came to trial.
Two of the four, journalists Neville Thurlbeck and Greg Miskiw, were each given a six-month prison sentence, reduced in part from what it could have been in light of their guilty pleas, the judge said.
Journalist James Weatherup received a four-month sentence, suspended for a year, and 200 hours of community service. A suspended sentence means he should not go to prison unless he breaks the law in that time.
Private investigator Glenn Mulcaire was given a six-month prison sentence, suspended for a year, and was also ordered to do 200 hours of community service.
Sentencing Mulcaire, the judge described him as "lucky." The sentence was complicated by the fact that he had already been sent to prison for six months for phone hacking in 2007. This trial involved additional charges.
The judge said that besides Mulcaire, the defendants "are distinguished journalists who had no need to behave as they did to be successful" but that their reputations in fact aided their wrongdoing.
"They all achieved a great deal without resorting to the unlawful invasion of other people's privacy. Those achievements will now count for nothing."
He added, "All three have expressed remorse for what they have done. I am afraid that that has the appearance of regret for the consequences, both to them and others, of getting caught, rather than true remorse."
Coulson, Thurlbeck and Miskiw are all in custody and will start their sentences immediately.
Victims of hacking
In his remarks to the court, the judge also recognized the controversy surrounding the case.
"There will be those who will be outraged that I haven't passed sentences well in excess of the permitted maximum," he said, "and there will be those that think that it shouldn't be a crime for the press to intrude into the lives of the famous and that the legislation and this prosecution is in some way an attack on the freedom of the press to carry out their vital role as public watchdogs."
He also focused on the impact on the thousands of victims of phone hacking -- who were not just those who put themselves in the public eye.
"Targets of phone hacking were politicians, celebrities and royalty. In addition, there were people who were targeted simply because they were friends of, worked with or were related to famous people," the judge said.
Journalists in search of stories listened to "intensely personal" messages that should have remained private, he said.
As a result, information "ended up as front page exclusives and caused serious upset and distress to the subjects and to those close to them," he said. It also fostered an "undercurrent of distrust" between friends and family who -- unaware of the News of the World's practices -- suspected each other of selling the information.
He also commented on the News of the World's "unforgivable" hacking of the voice mail of murdered teenager Milly Dowler.
"The fact that they delayed telling the police of the contents of the voice mail demonstrates that their true motivation was not to act in the best interests of the child but to get credit for finding her and thereby sell the maximum number of newspapers," he said.
The 168-year-old newspaper was closed down in 2011 in the wake of public outrage prompted by the hacking of Dowler's phone.
Joan Smith of the media reform campaign group Hacked Off said the sentences had a "symbolic importance" beyond the individual penalties.
"I don't think the length of the sentences really matters very much," she told CNN. "It's the fact that a court has said that this is not just unacceptable, but against the law.
"So it means as a society we are saying that we don't think that this behavior should happen and it will be punished."
Retrial on additional charges
Coulson faces a retrial on two charges of conspiring to commit misconduct in a public office after the jury was unable to reach a decision.
The newspaper's ex-royal editor, Clive Goodman, also faces a retrial on the same charges. Both have pleaded not guilty.
Coulson resigned from the Sunday tabloid in January 2007 after its then-royal editor, Goodman, and Mulcaire were jailed for hacking into voice-mail messages left for royal aides.
Coulson said he knew nothing about the hacking but resigned because he was editor of the paper at the time.
In that July, then-opposition leader Cameron hired Coulson as his director of communications. Cameron became British Prime Minister in 2010, and Coulson moved with him to Downing Street.
In January 2011, Coulson resigned from his post as coverage of the phone hacking scandal broadened. He insisted he was innocent but said he had become a distraction for the government.
Cameron apologized in Parliament last week for hiring Coulson, saying it had been "the wrong decision."
Another of Murdoch's former newspaper chiefs, Rebekah Brooks, was cleared of all charges after the eight-month trial at the Old Bailey court. Her husband and three others were also cleared of all the charges against them.
CNN's Erin McLaughlin contributed to this report.