Phillips has missed the club's last four games due to a hamstring injury, having not featured since the 2-2 draw with West Ham United in February. Chadli and Rondon meanwhile have been on international duty with Belgium and Venezuela respectively.
Chadli played 90 minutes in the 1-1 draw with Greece on 25 March, starting again away to Russia three days later before he was replaced by Yannick Ferreira Carrasco after 77 minutes having suffered a suspected shoulder injury.
Rondon meanwhile started and completed both of Venezuela's World Cup 2018 qualifiers against Peru and Chile, with Baggies boss Tony Pulis still to decide whether the globetrotting pair will be ready for Saturday's clash at Old Trafford.
"We still don't think Matt will be fit," Pulis told a press conference on Friday. "Salomon is back today, it is the first time we have seen him. He had the longest and furthest to travel over this period.
"Chadli came off with a shoulder injury in Russia. So he'll assess him today before the game tomorrow. I think Salomon will be okay, it's just the journey and the two games he played."
While West Brom have doubts over three key players, Manchester United also return from the international break with a host of injury concerns.
Both Phil Jones and Chris Smalling picked up injuries during the international break with Jose Mourinho confirming this week the defensive pair will be unavailable Saturday. Paul Pogba meanwhile is not ready to return after suffering a hamstring injury in the Europa League victory over FC Rostov, with Ander Herrera and Zlatan Ibrahimovic are suspended.
West Brom have also won on their last two of their last three trips to Old Trafford, recording 2-1 and 1-0 wins over the Premier League giants in the 2013-14 and 2014-15 campaigns.