Phillips was born and raised on the family farm between Bancyfelin and St Clears, He spent his late teenage years as both a blind and open side flanker at Whitland RFC before moving to Carmarthen RFC playing at scrum-half.
Phillips made his first appearance for the Scarlets at the age of 20, and remained there in spite of restrictions in first team appearances due to the performances of Dwayne Peel, until the summer of 2005.
Phillips represented Wales at Under 21 level where he played with fellow Cardiff player Nicky Robinson. In 2003 he made his Wales debut against Romania and scored a try.Phillips toured Argentina and South Africa in 2004, and also scored during the 2005 tour of the USA and Canada.
In 2008, Wales appointed a new coach, Warren Gatland, who liked Phillips' physical presence. He forced his way into the Welsh team against England, for the 2008 Six Nations Championship. He scored the winning try as Wales claimed a 26–19 victory – their first at Twickenham in 20 years
Mike Phillips started all three Tests during the 2009 British & Irish Lions tour of South Africa and has since secured two RBS 6 Nations winners’ medals The scrum-half started every match of Wales’ latest Championship success and returned to his best with a rousing performance against England.
He played in six matches in South Africa, including all three Tests, and he scored in the opening encounter with the Springboks in Durban. Since 2009 he has remained one of the first names on Gatland’s team-sheet and he started every clash of Wales’ consecutive Championship crowns.
On 16 March 2013 Phillips surpassed the record of 76 caps set by Dwayne Peel as the most capped scrum-half for Wales. Tall and powerful, unusual properties in a scrum half, he has been compared to ex-Wales international Terry Holmes.