City drew 2-2 with Leeds at the KC Stadium, conceding a late equaliser to Stuart Dallas, as their automatic promotion hopes ended.
The top two was deemed by some as a formality at Christmas time, but Hull have stuttered in the second half of the season and Phelan knows where work needs to be done.
“There have been ups and downs, we’ve been on decent runs and then got back on track after bad ones,” the assistant manager said.
“At the moment we are concerned we are giving away a couple of goals a game, because if you’re scoring two and not winning... We need to find a remedy, which we will do. We will prepare and discuss how we’re going to do that.
“We need to make sure everybody knows their jobs in the next three weeks.”
Phelan and City boss Steve Bruce watched on as Abel Hernandez and Tom Huddlestone scored in first-half injury time to cancel out Chris Wood’s opener for Leeds.
Wood then missed a penalty before Dallas’ leveller, which stretched Leeds’ unbeaten run to four games and added weight to Steve Evans’ bid to earn a new deal off controversial owner Massimo Cellino.