The 21-year-old has impressed since joining the Tangerines from Wycombe two years ago, plundering 18 goals for the npower Championship side last season.
Phillips' form has seen him linked with a move away from Bloomfield Road, with the south coast club strongly linked as a potential destination.
Press Association Sport understands that Southampton have firmed up their interest in the winger and made a £6million bid for the Scotland international.
The move comes just days after Blackpool boss Ian Holloway pledged to report an unidentified club he claimed made an illegal approach for Phillips.
Some reports named Southampton as the team in question, forcing Saints boss Nigel Adkins to deny such a move.
"It's a shame that Blackpool have had to go and do things via the media in the way that they have done," he told the club's official website, www.saintsfc.co.uk.
"I don't think there is any hiding from the fact that Matt is a player that we have been an admirer of for the past few years, and I think in the last couple of weeks he has probably been identified as a target for a number of teams in the Premier League.
"I know that from the chairman's point of view he has been in contact with the Blackpool chairman and that we have had a conversation with their chief executive, and I have spoken to Ian Holloway myself, so it's not as if there has not been an interest demonstrated from Southampton.
"As I have said, we like to think that we do everything properly, by the book and we will continue to do our matters privately and behind the scenes. Obviously this situation has now arisen and we will take action on that and respond in the appropriate manner."