I dont do any resizing at all, so there really shouldnt be any problem.

each sprite is 24x32pixels, and 24 does not add up to 256.

i dont see any reason for having spritesheets that are uniform in sixe either, as long as the sprites fit and have the correct spacing.
(mine is automatically created, so sizing and spacing is allways correct)

I have used these spritesheets with unDelphiX and Gamemaker, and they work there, so why not with phoenix?

heres a pic of the char as it is in phoenix, and they way it should be