The 2005-born centre-back broke into the Rovers' first team under Jon Dahl Tomasson last season, making 14 appearances for the Championship side in total.
Phillips started five Championship matches for Blackburn, who finished seventh in the table and only missed out on a spot in the playoffs on goal difference.
The 6ft 3in defender also made three FA Cup appearances as Tomasson's side reached the quarter-finals, as well as starting two matches in the EFL Cup, where his side lost to Nottingham Forest in the fourth round.
A former Wales youth international, Phillips has since represented England from Under-17 level and has played every minute of the Under-19s last six European Championship qualifying matches.
Phillips's breakthrough had apparently attracted the attention of both Manchester United and Chelsea, although Blackburn tied the teenager down to a new contract until 2025 last year.
However, according to journalist James Nursey, Tottenham have beaten their Premier League rivals to the signing of Phillips, whose arrival in North London should be finalised on Wednesday.
Nursey adds that Phillips will immediately fly out to Asia in order to link up with Ange Postecoglou's team, who lost 3-2 to West Ham United in their opening pre-season friendly in Perth on Tuesday.
The England Under-19 international could therefore be in line for an immediate debut against Leicester City in Thailand on July 23, or he may alternatively earn his first minutes against Lion City Sailors in Singapore on July 26.
Despite only tying Phillips a new deal less than a year ago, Blackburn could now face a mass exodus of players and staff after
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