Boro had agreed an initial fee of around £7m with Tottenham for the 21-year-old defender and were also ready to sign off on a series of potential add-ons that Spurs officials had wanted to include as part of the deal.
Phillips is understood to have visited Boro’s Rockliffe Park training ground at the end of last week in the hope of a transfer being finalised over the weekend.
However, as the situation has developed, so all parties have decided to pause discussions with some elements of the proposed transfer still to be completed.
The deal is not off, with Boro officials expected to hold further talks with Phillips and his representatives and the hierarchy at Spurs in the next few days.
As things stand though, all parties are considering their options ahead of the start of the Championship season next weekend.
Manchester-born Phillips began his career in the youth set-up at Blackburn Rovers before making a £2m move to Tottenham in the summer of 2023.
He spent the second half of the 2023-24 season on loan at Plymouth Argyle, and has had two loan spells with Stoke, making 83 senior appearances for the Potters.
Boro confirmed the signing of goalkeeper Radek Vitek from Manchester United yesterday, with the Czech shot-stopper available to make his debut in Saturday’s Championship season-opener against Lincoln City.