The national health body is asking people in Scotland to “to defer such parties at this time”, saying that a number of outbreaks have been linked to parties.
PHS is warning that not enough it known about how much protection the vaccines offer against Omicron.
Dr Nick Phin, Director of Public Health Science and Medical Director, PHS said: “There is much that we still need to learn about Omicron, but early evidence suggests that this new Covid variant is much more transmissible.
"The impact of this transmissibility has been seen in recent weeks, with a number of Omicron outbreaks linked to parties.
“We still need to learn more about the severity of disease caused by Omicron and the effectiveness of vaccines, but there are important things that we can do to help protect ourselves and our families now.
"To help minimise the further spread of Covid-19, and Omicron in particular, I would strongly urge people to defer their Christmas parties to another time.
“I appreciate that everyone is keen to celebrate this festive season, particularly after the pressures of the last twenty months, but by postponing some plans we can all do our bit to protect ourselves and our loved ones.”
The call comes as Scotland has reported another new Omicron case, bringing the total to 109.
Latest Scottish Government figures also showed there were 16 coronavirus deaths and 3,196 cases recorded within the past 24 hours.
The Covid-19 death toll in Scotland under the daily measure – of people who first tested positive for the virus within the previous 28 days – now stands at 9,688.
PHS is also reminding Scots to get their vaccination and booster, take a test each time they are socialising with people out with their household.
The latest statistics on Thursday said a total of 4,358,725 people have received their first dose of a Covid-19 vaccination in Scotland, 3,967,477 have received their second dose, and 2,000,915 have received a third dose or booster.