Forest boss Billy Davies
The Reds striker fired over from the spot on 63 minutes in this FA Cup third round tie at the City Ground.
And it proved costly, as the game ended 0-0, setting up a replay in ten days time.
Forest were again impressive and the draw did extend their unbeaten run to 17 matches.
Billy Davies' side could have had the lead after just two minutes, Chris Cohen playing in Dexter Blackstock, but on the turn, he fired into the side netting from a tight angle.
Shortly after, Rob Earnshaw was fed the ball by Cohen but from 20 yards out, Joe Hart saved his low effort.
It was then Cohen's turn to find himself in space when Chris Gunter's cross fell to him at the back post but after getting the ball out of his feet, he could not find Earnshaw in the six-yard box when he fired in a cross.
Then at the other end, Lee Camp got down to save from Cameron Jerome before former Forest loanee, Gary McSheffrey, came on to replace Stuart Parnaby.
Paul McKenna put Forest on the front foot again when he stole possession and he teed up Earnshaw, whose driven shot was straight at Hart.
Camp was sent scrambling to his right to keep out a shot from Phillips shortly after the half hour mark before Birmingham lost a second player to injury, this time Lee Carsley being carried to the dressing room with a knee problem.
Just before the break, Chambers rose to meet Majewski's corner but it crashed back out off the underside of the bar.
Five minutes after the interval, a deflected shot fell kindly to Jerome but from six yards out, Camp dived brilliantly to scoop the ball away from the striker when he looked set to score.
Forest should have scored when Blackstock poked the ball to his right for the onrushing Cohen but with just Hart to beat, he fired at the Blues' goalkeeper.
On 62 minutes, Anderson was fouled in the box by Gregory Vignal but from the penalty spot, Earnshaw fired over the bar.
He almost made amends minutes later when he produced a superb flick which Blackstock laid back into his path but after going clear, Hart pulled off a great one-handed save to turn it around his far post.
At the other end, Birmingham almost made the Reds pay but Phillips' 25-yard shot cannoned off the far post with Camp beaten.
Birmingham hit Forest on the break and when Phillips was picked out in space, Camp pounced to save before McSheffrey fired the follow up into the Bridgford Stand.
After being the dominant side, Forest had to withstand some pressure late on but neither side could find the decisive strike.
FOREST: Camp, Perch, Gunter, Chambers, Morgan, Anderson (Tyson, 68), Cohen, McKenna, Majewski, Earnshaw (McCleary, 79), Blackstock (Adebola, 85). Subs: Wilson, Smith, McGugan, McGoldrick
BIRMINGHAM: Hart, Ridgewell, Vignal, Parnaby (McSheffrey, 21), R Johnson, S Johnson, Ferguson, Fahey, Carsley (Bowyer, 39 mins), Phillips (Benitez, 85), Jerome. Subs: Doyle, Taylor, McFadden, Queudrue
Referee: Steve Bennett (Kent)
Attendance: 20,975 (4,485 away fans)