Phillips was an ever-present in the England team that reached the final of Euro 2020, but has played just 13 minutes in a City shirt since joining from Leeds in July.
The 26-year-old has been sidelined since September after undergoing surgery on a long-running shoulder problem.
Kyle Walker is also a doubt for the World Cup as he races to recover from a groin injury and will not be involved against Chelsea.
England manager Gareth Southgate will name his squad for the tournament in Qatar on Thursday.
"It is up to Gareth," said Guardiola on whether the duo will be fit for the World Cup.
"They are communicating with physios, and doctors and the English national team. Kalvin will be with the squad for the Chelsea game."
Erling Haaland will not be heading to the World Cup as Norway failed to qualify, but could be rested by Guardiola in midweek as he recovers from a foot ligament injury.
Haaland came off the bench to score a 95th minute penalty to beat Fulham 2-1 on Saturday.
City have one more Premier League game, at home to Brentford on Saturday, before a five-week break for the World Cup.
"He is still not perfect," added Guardiola on Haaland, who has scored 23 goals in 16 appearances for City.
"We will see tomorrow and Saturday. He is getting better.
"The main thing is the bone was not broken – the ligament is damaged a little bit, so he's still not perfect right now."
City were drawn against RB Leipzig in Monday's draw for the last 16 of the Champions League.
The English champions are favourites to finally end their quest to win European club football's biggest prize.
But Guardiola believes the hangover from the World Cup will play a major part on who progresses in the Champions League come February.
"After the World Cup, we will start again," he said.
"We need to see how we are in that moment. If we play next week against Leipzig, I could tell you how we are exactly - but in February, many things can happen."
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)