The Teessiders have been active in the transfer market this summer, reinvesting money from the sale of Hayden Hackney and the sell-on windfall from Morgan Rogers' £117million move to Chelsea.
As a result, Rovers will be due a small windfall due to their own clauses inserted in the deal that saw him join Tottenham Hotspur in the summer of 2023.
Spurs paid £2.5m for Phillips, who had clauses in his contract dictating the price to a potential buyer based on his appearances for the first team. Agreeing to those terms was how Rovers got the England youth international to sign his first professional contract and would've received far less in compensation.
Boro have agreed an initial £7m deal for Phillips and, as previously reported, Lancashire Telegraph believes Rovers' sell-on to be 15 per cent of profit.
Rovers would therefore be entitled to around 675K, which is paid in instalments rather than a lump sum, as with any transfer fee.
It has been widely reported that there are a number of add-ons and future clauses which could see that figure rise significantly, to as high as potentially £20m.
For the fee to reach anything like that figure, it would likely be contingent on Middlesbrough's promotion and Phillips featuring for England. That's not to say there won't be more achievable triggers, which we're obviously not privy too.
Boro have structured several deals in that manner this summer. Will Lankshear's move from Spurs was also an initial fee of around £10m, rising to £20m. They are also signing Radek Vitek from Manchester United for an initial £7m, which could rise to eight figures.
Phillips came through the ranks at Rovers and made his first-team debut under Jon Dahl Tomasson in 2022/23, making 14 appearances as a teenager.
Having moved to Spurs, he then joined Plymouth Argyle the following January before spending the last two seasons on loan at Stoke City, racking up more than 100 Championship appearances.
Rovers host Middlesbrough in their first home game of the season on August 22.