It depends whether it is a mono- or polymicrobial bioflim. If the latter there is not much chance of success. I would suggest looking at Ian Connerton's work on 'phage treatment of carcasses for foodborne pathogens as a starting point.
phages are highly specific for their host so this thing in mind when you are going to treat your biofilm with phage
you can prevent the biofilm formation by adding host specific phage at initial stage and you can also prevent or eradicate the established biofilm by the application of phage