I was wondering how much strong was Phillidor.

For a relative comparation, what fide rating could he receive these days??

around 2400????

It's pretty hard to tell.  As I understand it, we only have a scattering of his games played when he was older, so we have nothing of him in his prime to look it.  Also we don't really know how good his opposition was either (which makes it doubly hazardous to hazard a guess).  He was however the first player to analyze the R + B vs. Rook endgame in any depth, which takes a strong master to do.

Really, when you go back that far I don't think questions of rating mean very much, since ratings depend a great deal on having a very large reservoir of good players  to play and get rating points from--and Philidor was denied that opportunity.  He was though as I understand it head and shoulders above anybody else in the 18th century.