The Cardinal Newman College scholar has won a place and funding to study in Pennsylvania.
Her accolade comes after the 17-year-old took part in the Sutton Trust US Programme, run in partnership with the US-UK Fulbright Commission.
Last summer, Phoebe was one of 150 students to take part in a summer school at Yale University and had a chance to visit several other US universities.
Students benefitted from an intensive programme of support administered through the US-UK Fulbright Commission.
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This included help with applications, college choices and admissions tests.
Since leaving St Michael’s High School in Chorley in 2014, she has taken part in the Sutton Trust US Programme.
She said: “I am now an ambassador and a team leader for the programme so I would love for as many people as possible to be made aware of this life changing programme.”
Phoebe, who will spend four years in the USA added: “This programme has given me opportunities which have changed my life.
“I have made lifelong friends and have even been able to give back to the programme and help the next cohort of Sutton Trust Students as a Team Leader.
“The Sutton Trust has given me a chance to live my dream of studying at Bryn Mawr while also opening up my future to endless possibilities.”
She is one of 66 students who won a place to study in the US through the Sutton Trust US Programme and will fly out on her 18th birthday - the day before her A -level results are published.
Phoebe, f‑rom Whittle-le-Woods, near Chorley, studied maths, biology, psychology and EPQ at Newman.
Besides being a student mentor and an ambassador for CAFOD, she is active in raising awareness of autism taking part in charity events including two half marathons.
Pheobe was a youth volunteer for the Archdiocese of Liverpool pilgrimage to Lourdes and volunteers at an art club for the disabled.
She will be studying psychology, international relations, economics and art in the US.