One of the stars of the 2009 Lions tour, Phillips was suspended the Friday before last following a late-night altercation outside a fast food restaurant in the Welsh capital.
The former Scarlets, Blues and Ospreys No9, who recently signed for French Top 14 outfit Bayonne, was pictured being restrained by security staff in the city centre in the early hours of the morning on Tuesday, June 14.
Phillips was initially told not to report to Welsh training indefinitely but head coach Warren Gatland and the Welsh Rugby Union have now lifted his suspension after the player insisted there would be no repeat of his behaviour.
And after apologising to his coaches, team-mates and Wales supporters alike, Phillips will now report to the WRU National Centre of Excellence to complete supervised fitness, conditioning and skills training from tomorrow.
"I deeply regret my behaviour," said Phillips.
"I have formally and sincerely apologised to my teammates and the coaching staff in the Welsh rugby squad and would like to take this opportunity to do exactly the same to the Welsh rugby public and anyone else who has been offended by this or other episodes.
"As a player I'm really passionate and never back down. I know I can't allow that part of my character to come to the surface off the rugby pitch.
"I have realised I have an issue with the way in which I deal with, and have dealt with, the pressures of my current environment and have sought, and will continue to seek, help and advice in relation to that issue.
"I am a professional rugby player and I give the game my all, but there have been times I have let myself down as well as my family, the fans and my team-mates.
"This is the most embarrassing thing that has happened to me in my career. I am ashamed to have let myself get into this kind of situation and I am determined to put things right."
An extended suspension would have left Phillips in danger of missing Wales' pre-World Cup training camps in Poland, with Gatland and conditioning coach Adam Beard stating that any players who didn't take part in those get togethers would be behind the eight ball when it comes to selection for the tournament itself.
A Wales World Cup squad without one of its biggest names would have been a major surprise, though, and Gatland will be a happier man for Phillips' apology.
"Mike clearly breached the disciplinary code of conduct we have in place and was dealt with decisively and properly," said Gatland.
"We have taken into account all the relevant issues and Mike's apology in taking the decision to reinstate him in the extended RWC squad.
"An important factor in allowing Mike back into the squad was his decision to actively seek help to resolve his behavioural issues."