B737NG Captain reported a speed deviation approaching ORD; citing communication difficulties and spacing concerns as contributing.

Narrative

Arriving into Chicago we had questioned Chicago Center about an aircraft ahead because we were experiencing wake turbulence. Was told it was an ERJ and they kept our spacing tight all the way into the arrival. We were on base to Runway 10R for the LOC Y 10R approach. We were at 210 then told to turn to a heading and intercept the 10R localizer. Upon intercepting the localizer we were set up the approach for the 10R localizer using VNAV. We were told to slow to 170 and contact Tower at Flynn. [We selected] the gear down to begin slowing. With the increased workload of joining the approach neither of us could confirm if we were to be 170 or a faster speed to Flynn . Going from 210 to a slower speed while in VNAV path and gear down the plane was having difficulty slowing so we went flaps 15. Approach was very busy; and we couldn't get a word in with Approach to confirm so we changed to Tower at Kevnn for landing clearance and we asked if they wanted 170 and were told whatever TRACON told us. We were told to go back to Approach and we changed over we told Approach we were slowing to 170 to Flynn since it looked like we were gaining on the aircraft ahead. They said 'Roger' and put us back to Tower. We then continued to slow and went to flap 40 ref speed of 143 that we had briefed because of the shorter runway and to allow more spacing with the aircraft ahead of us since we were very close the whole way in. We then got landing clearance again and landed with no issues.