Open the file and change the language in the menu. TM should
remember this new association, and treat .php as html or xhtml or
whatever you select in the future. In the main menu, I think, there
is a 'File associations' item or similar, displaying currently
it works well.
It is very useful alternate beetween php and xhtml syntax, ok!
Also option+control+shift+p and option+control+shift+h are good
things: I must read better the help files *soon* :-))
TextMate is wonderful.