Phibbs and Canadian International, Jebb Sinclair, come back in after missing the last two rounds of the Amlin cup.
London Irish Director of Rugby Brian Smith said: "Our opponents on Sunday are also joint top of their Pool so like us they have a lot to play for. Worcester have a very strong squad and we're expecting an epic cup battle."
London Irish team to face Worcester Warriors:
15. Tom Homer; 14. Topsy Ojo*; 13. Guy Armitage; 12. Sailosi Tagicakibau*; 11. Marland Yarde; 10. Shane Geraghty* (Captain); 9. Pat Phibbs; 1. Max Lahiff; 2. Mike Mayhew; 3. Halani Aulika*; 4. George Skivington; 5. Bryn Evans*; 6. Matt Garvey; 7.Jebb Sinclair*; 8. Chris Hala'ufia*
Replacements: 16. Davey McGregor; 17. Jerry Yanuyanutawa*; 18.Leo Halavatau; 19. Kieran Low; 20. Alex Gray; 21. Anthony Watson; 22. Ian Humphreys; 23. Jack Moates
*Denotes Internationals
London Irish has signed Mike Mayhew and Davey McGregor on short term loan deals from Newcastle and Coventry respectively.
