Phillips was born in Pretoria and represented the Blue Bulls at the Under-16 Grant Khomo Week in 2011 and at the Under-18 Craven Week in 2012 and 2013. In both 2012 and 2013, he was included in a South Africa Schools squad after the Craven Week tournament. In 2012, he started matches against France[2] and England,[3] while in 2013, he started against England[4] and came on as a replacement against Wales.[5]
After high school, he moved to Cape Town to join the Western Province Rugby Institute. He started nine matches for the Western Province U19 team during the 2014 Under-19 Provincial Championship, scoring four tries. His first try came in a 21–20 win over Eastern Province U19[6] before scoring two tries in a 43–24 victory over the Leopards U19s in Potchefstroom.[7] His fourth try came in their 29–22 victory over Free State U19 in the semi-finals[8] to send them to the final, which they also won, beating Phillips' old side the Blue Bulls 33–26.[9]
He made his first class debut during the 2015 Vodacom Cup, coming on as a replacement for Western Province in their 32–12 victory over a Sharks XV.[10] Three more appearances off the bench followed during the play-offs, in victories over a Leopards XV in the quarter finals[11] and the Blue Bulls in the semi-finals,[12] as well as in their 7–24 defeat to the Pumas in the final of the competition.[13]
Phillips made twelve appearances for Western Province U21 in the 2015 Under-21 Provincial Championship, scoring tries against Golden Lions U21,[14] Blue Bulls U21,[15] Leopards U21[16] and a brace in their return leg against the Blue Bulls in Cape Town[17] to help his side finish top of the log.[18] He was also in the starting line-up for their semi-final victory over the Golden Lions[19] and their victory in the final over the Free State[20] to win a youth title for the second year in a row.
He appeared for Western Province in the 2016 Currie Cup qualification series, scoring tries in matches against a Free State XV,[21] the Eastern Province Kings[22] and the Griffons.[23]