And the team sitting third bottom of the Scottish Professional Football League stunned the side who are third top when Philips struck a first-time effort from 18 yards to seal a 1-0 win.
The Coatbridge side had not beaten Motherwell outside the Lanarkshire Cup in 34 meetings in the league and Scotland's two major cup competitions.
And they ceded home advantage by moving the tie to New Douglas Park, with the Motherwell support forming the vast majority of the 2,950 crowd.
Motherwell named a strong team with Keith Lasley and John Sutton the only regulars rested from the start, although Iain Vigurs and Lionel Ainsworth missed out through injury.
But they lacked urgency and struggled to get in behind a solid Rovers team that sat back and soaked up the pressure.
The game was briefly held up in the early stages when a smoke bomb was thrown on to the pitch from the Motherwell support.
Their team were lacking a spark and, apart from several runs from Zaine Francis-Angol, did not threaten to break through before Rovers wide player Liam Cusack got the first shot on target in the 20th minute, a curling effort that Gunnar Nielsen tipped over at full stretch.
Motherwell were otherwise dominating territory but could not trouble goalkeeper Neil Parry. Bob McHugh headed over under pressure following Fraser Kerr's cross and Stuart Carswell dragged a shot wide from the edge of a crowded box.
And Rovers had the best chance of the half when Gary Philips' bouncing cross reached Chris Dallas, who got in ahead of Shaun Hutchinson but could not keep his half-volley down.
Cusack charged down McHugh's effort after a good break from midfielder Paul Lawson and Sutton replaced the striker at half-time.
Motherwell got their first effort on target just after the restart but Lawson's powerful strike took a deflection that saw the ball loop into the hands of Parry.
But Stuart McCall's half-time team talk did not have the desired effect and the Motherwell boss made a double switch in the 71st minute when he brought on skipper Lasley and midfielder Jack Leitch, the son of former Motherwell captain and current head of youth Scott Leitch, with wide players McFadden and Francis-Angol exiting.
But the Scottish Premiership side had another scare when Mark McGuigan beat Steven Hammell on the right wing and fired just wide of the near post.
Motherwell finally forced Parry into some serious action in the 78th minute when Sutton met Lawson's corner from four yards with a powerful header but the Rovers goalkeeper proved up to the task with a save to match his name before scrambling the ball to safety.
Motherwell belatedly found the urgency that McCall would have wanted from the start but their League Two opponents continued to defend stoutly.
And they stunned Motherwell when Ryan Tiffney laid the ball back for Phillips to fire a left-footed shot into the corner of the net with Nielsen getting a hand to the ball but being unable to keep it out.
Anier had a good chance in injury-time when the ball fell for him in the box but he sliced well wide and the Motherwell fans vented their anger at McCall and the players before applauding the underdogs as they celebrated with their joyous band of supporters.
- Sports & Recreation
- John Sutton