Phillips could be pulled into the England squad if any of the 18-strong squad withdraw.
Wycombe boss Gary Waddock said: "It's fantastic news both for Matt and the club. I'm really pleased for him."
Head of youth development Richard Dobson, who has played an important part in Phillips's career, said: "It's a great testament to Matt's ability and attitude.
"People forget that Matty is only 19 and still developing and the manager has been clever in the way he has used him. This is something the club can be very proud of."
England will be playing three games in Ukraine at the end of May.
They face the Republic of Ireland, Bosnia-Hercegovina and Ukraine in group three.
The winners of each group will progress to the eight-team European Under-19 Championship final tournament in France in July.
Source: BBC Sport
Source: BBC Sport